{"id":4348,"date":"2020-11-19T20:58:42","date_gmt":"2020-11-19T15:28:42","guid":{"rendered":"https:\/\/golangbyexamples.com\/?p=4348"},"modified":"2021-01-15T23:22:05","modified_gmt":"2021-01-15T17:52:05","slug":"packages-modules-go-first","status":"publish","type":"post","link":"https:\/\/golangbyexamples.com\/packages-modules-go-first\/","title":{"rendered":"Packages and Modules in Go (Golang) &#8211; Part 1"},"content":{"rendered":"\n<p class=\"has-medium-font-size\">This is the chapter 4 of the golang comprehensive tutorial series. Refer to this link for other chapters of the series &#8211; <a href=\"https:\/\/golangbyexamples.com\/golang-comprehensive-tutorial\/\">Golang Comprehensive Tutorial Series<\/a> <br><br><strong>Next Tutorial<\/strong> &#8211; <a href=\"https:\/\/golangbyexamples.com\/packages-modules-go-second\/\">Packages and Modules &#8211; Part 2<\/a><br><strong>Previous Tutorial<\/strong> &#8211; <a href=\"https:\/\/golangbyexamples.com\/workspace-hello-world-golang\/\">Set up GO Workspace and Hello World Program<\/a><\/p>\n\n\n\n<p class=\"has-medium-font-size\">Now let&#8217;s check out the current tutorial. Below is the table of contents for the current tutorial.<\/p>\n\n\n\n<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_17 counter-hierarchy counter-decimal ez-toc-light-blue\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\">Table of Contents<\/p>\n<span class=\"ez-toc-title-toggle\"><a class=\"ez-toc-pull-right ez-toc-btn ez-toc-btn-xs ez-toc-btn-default ez-toc-toggle\" style=\"display: none;\"><i class=\"ez-toc-glyphicon ez-toc-icon-toggle\"><\/i><\/a><\/span><\/div>\n<nav><ul class=\"ez-toc-list ez-toc-list-level-1\"><li class=\"ez-toc-page-1 ez-toc-heading-level-1\"><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/golangbyexamples.com\/packages-modules-go-first\/#Overview\" title=\"Overview\">Overview<\/a><\/li><li class=\"ez-toc-page-1 ez-toc-heading-level-1\"><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/golangbyexamples.com\/packages-modules-go-first\/#Modules\" title=\"Modules\">Modules<\/a><\/li><li class=\"ez-toc-page-1 ez-toc-heading-level-1\"><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/golangbyexamples.com\/packages-modules-go-first\/#Before_Modules_World\" title=\"Before Modules World\">Before Modules World<\/a><ul class=\"ez-toc-list-level-2\"><li class=\"ez-toc-heading-level-2\"><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/golangbyexamples.com\/packages-modules-go-first\/#Pre_Go_version_111\" title=\"Pre Go version 1.11\">Pre Go version 1.11<\/a><\/li><li class=\"ez-toc-page-1 ez-toc-heading-level-2\"><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/golangbyexamples.com\/packages-modules-go-first\/#In_Go_version_111\" title=\"In Go version 1.11\">In Go version 1.11<\/a><\/li><li class=\"ez-toc-page-1 ez-toc-heading-level-2\"><a class=\"ez-toc-link ez-toc-heading-6\" href=\"https:\/\/golangbyexamples.com\/packages-modules-go-first\/#After_Go_Version_113\" title=\"After Go Version 1.13\">After Go Version 1.13<\/a><\/li><\/ul><\/li><li class=\"ez-toc-page-1 ez-toc-heading-level-1\"><a class=\"ez-toc-link ez-toc-heading-7\" href=\"https:\/\/golangbyexamples.com\/packages-modules-go-first\/#Understanding_Package_and_Also_Creating_a_module\" title=\"Understanding Package and Also Creating a module\">Understanding Package and Also Creating a module<\/a><\/li><li class=\"ez-toc-page-1 ez-toc-heading-level-1\"><a class=\"ez-toc-link ez-toc-heading-8\" href=\"https:\/\/golangbyexamples.com\/packages-modules-go-first\/#Creating_an_application_before_Module\" title=\"Creating an application before Module\">Creating an application before Module<\/a><\/li><li class=\"ez-toc-page-1 ez-toc-heading-level-1\"><a class=\"ez-toc-link ez-toc-heading-9\" href=\"https:\/\/golangbyexamples.com\/packages-modules-go-first\/#Exported_vs_Unexported_Names\" title=\"Exported vs Unexported Names\">Exported vs Unexported Names<\/a><\/li><li class=\"ez-toc-page-1 ez-toc-heading-level-1\"><a class=\"ez-toc-link ez-toc-heading-10\" href=\"https:\/\/golangbyexamples.com\/packages-modules-go-first\/#Nested_Packages\" title=\"Nested Packages\">Nested Packages<\/a><\/li><li class=\"ez-toc-page-1 ez-toc-heading-level-1\"><a class=\"ez-toc-link ez-toc-heading-11\" href=\"https:\/\/golangbyexamples.com\/packages-modules-go-first\/#Aliasing_in_importing_packages\" title=\"Aliasing in importing packages\">Aliasing in importing packages<\/a><\/li><li class=\"ez-toc-page-1 ez-toc-heading-level-1\"><a class=\"ez-toc-link ez-toc-heading-12\" href=\"https:\/\/golangbyexamples.com\/packages-modules-go-first\/#Init_Functions\" title=\"Init Functions\">Init Functions<\/a><\/li><li class=\"ez-toc-page-1 ez-toc-heading-level-1\"><a class=\"ez-toc-link ez-toc-heading-13\" href=\"https:\/\/golangbyexamples.com\/packages-modules-go-first\/#Order_of_execution_of_a_Go_program\" title=\"Order of execution of a Go program\">Order of execution of a Go program<\/a><\/li><li class=\"ez-toc-page-1 ez-toc-heading-level-1\"><a class=\"ez-toc-link ez-toc-heading-14\" href=\"https:\/\/golangbyexamples.com\/packages-modules-go-first\/#Blank_Identifier_in_import\" title=\"Blank Identifier in import\">Blank Identifier in import<\/a><\/li><li class=\"ez-toc-page-1 ez-toc-heading-level-1\"><a class=\"ez-toc-link ez-toc-heading-15\" href=\"https:\/\/golangbyexamples.com\/packages-modules-go-first\/#Package_Naming_Convention\" title=\"Package Naming Convention\">Package Naming Convention<\/a><\/li><li class=\"ez-toc-page-1 ez-toc-heading-level-1\"><a class=\"ez-toc-link ez-toc-heading-16\" href=\"https:\/\/golangbyexamples.com\/packages-modules-go-first\/#Conclusion\" title=\"Conclusion\">Conclusion<\/a><\/li><\/ul><\/nav><\/div>\n<h1 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Overview\"><\/span><strong>Overview<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<p class=\"has-medium-font-size\">Package is a way of code reusability in GO. As the name suggests, it is a way of grouping related code. Go modules is a way of dealing with dependencies in golang.&nbsp;<\/p>\n\n\n\n<p class=\"has-medium-font-size\">Every GO source file (.go file) in a GO application file belongs to a package. That is why every <strong>.go<\/strong> file starts with.<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package <package_name><\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Above is called <strong>Package Declaration<\/strong>. Please note this term as this will be used throughout this tutorial.<\/p>\n\n\n\n<p class=\"has-medium-font-size\">All .go files present in the same directory will belong to the same package. A great misconception around packages is that package is the name of the directory which contains .go files. That is not correct. A directory is just a directory and the name of the package is what is present in <strong>Package Declaration<\/strong>. Then what is the importance of the directory name? It will be explained in the tutorial as we go along.<\/p>\n\n\n\n<p class=\"has-medium-font-size\">Package can be of two types.<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li><strong>Executable package<\/strong> &#8211; Only <strong>main<\/strong> is the executable package in GoLang. A .go file might belong to the main package present within a specific directory. We will see later how the directory name or the <strong>.go<\/strong> file name matters.&nbsp; The main package will contain a main function that denotes the start of a program. On installing the main package it will create an executable in the <strong>$GOBIN<\/strong> directory.<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li><strong>Utility package<\/strong>&#8211; Any package other than the main package is a utility package. It is not self-executable. It just contains the utility function and other utility things that can be utilized by an executable package.<\/li><\/ul>\n\n\n\n<h1 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Modules\"><\/span><strong>Modules<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<p class=\"has-medium-font-size\">Module is go support for dependency management. A module by definition is a collection of related packages with <strong>go.mod<\/strong> at its root.&nbsp; The <strong>go.mod<\/strong> file defines the<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Module import path.<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Dependency requirements of the module for a successful build. It defines both project&#8217;s dependencies requirement and also locks them to their correct version<\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">Consider a module as a directory containing a collection of packages. The packages can be nested as well. Modules provide<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Dependency Management<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>With modules go project doesn&#8217;t necessarily have to lie in the <strong>$GOPATH\/sr<\/strong>c folder.&nbsp;<\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">Also in addition to <strong>go.mod<\/strong> file go also keeps a <strong>go.sum<\/strong> file which contains the cryptographic hash of bits of all project&#8217;s dependent modules. This to make validate that your project&#8217;s dependent modules are not changed.<\/p>\n\n\n\n<h1 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Before_Modules_World\"><\/span><strong>Before Modules World<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<p class=\"has-medium-font-size\">Modules were introduced in go in version 1.11. Let&#8217;s see version wise changes to fully understand what was the limitations earlier and what has changed since modules<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Pre Go version 1.11 &#8211; Modules did not exist at all<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Go Version 1.11 &#8211; Modules was introduced but not finalized<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Go Version 1.13 &#8211; Modules was introduced<\/li><\/ul>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Pre_Go_version_111\"><\/span><strong>Pre Go version 1.11<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"has-medium-font-size\">Before modules go only had packages. $GOPATH location would have three directories<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>src<\/li><li>pkg<\/li><li>bin<\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">These were the problems which existed before the modules era<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>All Go project in <strong>$GOPATH\/src<\/strong> directory<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>No native dependency management support<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>All the dependency will be downloaded in the <strong>$GOPATH\/src<\/strong>&nbsp; directory without versioning<\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">Let&#8217;s look at each problem one by one:<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Any GO project has to be inside the <strong>$GOPATH\/src <\/strong>directory<\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">This was a big limitation in terms of that it restricted where you can keep your project.<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>No native dependency management support<\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">Also, one issue before modules was that there was no way to specify a dependency in a project. Alternate solutions such as dep, glide were available but a native solution was missing.<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>All the dependency will be downloaded in the $GOPATH\/src&nbsp; directory without versioning<\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">When we do a go get it will download the required package in the $GOPATH\/src directory.&nbsp; So before go version 1.11, below go get command<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">go get github.com\/pborman\/uuid<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">It will download the package at the location<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">$GOPATH\/src\/github.com\/pborman\/uuid<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Notice one thing about the go get command above that no version was specified. Hence it downloads the latest version present. Also, notice the downloaded package. Even it doesn&#8217;t list down any versioning info. Now, this is a problem. What if there is an update in the&nbsp; <strong><a href=\"http:\/\/github.com\">github.com<\/a>\/pborman\/uuid<\/strong> package and you want to get that update. Since there is no versioning the updated package will get downloaded at the same location replacing the older one.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"In_Go_version_111\"><\/span><strong>In Go version 1.11<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"has-medium-font-size\">In Go 1.11. modules were introduced but not finalized. So if you still using it then better to switch to the latest version<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"After_Go_Version_113\"><\/span><strong>After Go Version 1.13<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"has-medium-font-size\">We already discussed all the problems which existed before the pre-modules era. Now let&#8217;s see how each of these problems got resolved with the introduction of modules. <\/p>\n\n\n\n<p class=\"has-medium-font-size\">The first problem was<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>All Go project in <strong>$GOPATH\/src<\/strong> directory<\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">With modules, this is no longer a requirement.<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>No native dependency management support<\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">Modules introduced native dependency management within go. With modules, it provides two new files which are<\/p>\n\n\n\n<ol class=\"has-medium-font-size wp-block-list\"><li>go.mod<\/li><li>go.sum<\/li><\/ol>\n\n\n\n<p class=\"has-medium-font-size\">With <strong>go.mod<\/strong> and <strong>go.sum<\/strong> files we are able to install a precise version of a dependency without breaking anything. We already gave a brief introduction to these files at the beginning of this tutorial. Later in the tutorial, we will look at it in detail<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>All the dependency will be downloaded in the <strong>$GOPATH\/pkg\/mod<\/strong>&nbsp; directory with versioning<\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">So if you download a different version of the same library then both will be downloaded in a different directory inside <strong>$GOPATH\/pkg\/mod <\/strong>without overriding each other.&nbsp; <strong>$GOPATH\/pkg\/mod<\/strong>&nbsp; will have two things inside it<\/p>\n\n\n\n<ol class=\"has-medium-font-size wp-block-list\"><li><strong>cache<\/strong> &#8211; This is the folder where all dependencies will get downloaded along with the zipped code<\/li><li>Zipped code of all downloaded dependencies will get copied over from the cache directory.<\/li><\/ol>\n\n\n\n<p class=\"has-medium-font-size\">Also, there is a new env introduced named <strong>GO111MODULE<\/strong><\/p>\n\n\n\n<p class=\"has-medium-font-size\">When <strong>GO111MODULE=off<\/strong>, then go get will behave in the old way where it will download the dependency in the $GOPATH\/src folder.<\/p>\n\n\n\n<p class=\"has-medium-font-size\">When <strong>GO111MODULE=on<\/strong>, then go get will behave in a new way and all the modules will get downloaded in the <strong>$GOPATH\/pkg\/mod\/cache<\/strong> folder with versioning.<\/p>\n\n\n\n<p class=\"has-medium-font-size\">When <strong>GO111MODULE=auto<\/strong>, then<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>When running go get outside the $GOPATH\/src folder, then will behave as if it is GO111MODULE=on<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>When running go get inside the $GOPATH\/src folder, then will behave as if it is GO111MODULE=off<\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">Let&#8217;s now create a module. Whatever we discussed will be more clear then<\/p>\n\n\n\n<h1 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Understanding_Package_and_Also_Creating_a_module\"><\/span><strong>Understanding Package and Also Creating a module<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<p class=\"has-medium-font-size\">The below command can be used to create a module.<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">go mod init {module_import_path}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Let&#8217;s see <strong>go.mod<\/strong> and <strong>go.sum<\/strong> file again that we had discussed earlier<\/p>\n\n\n\n<p class=\"has-medium-font-size\"><strong>go.mod<\/strong><\/p>\n\n\n\n<p class=\"has-medium-font-size\">It is the module dependency file. It will have three things<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Import path of the module at the top<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>The version of go with which the module is created<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Direct dependencies of the module.<\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\"><strong>go.sum<\/strong><\/p>\n\n\n\n<p class=\"has-medium-font-size\">This file lists down the checksum of direct and indirect dependency required along with the version. It is to be mentioned that <strong>go.mo<\/strong>d file is enough for a successful build. The checksum present in <strong>go.sum<\/strong> file is used to validate the checksum of each direct and indirect dependency.<\/p>\n\n\n\n<p class=\"has-medium-font-size\">Now the question is what is <strong>import_path<\/strong>.&nbsp; <strong>import_path<\/strong> is the prefix path that will be used by any other module to import your module. We will learn more about the import path in the second part of the tutorial.<\/p>\n\n\n\n<p class=\"has-medium-font-size\">Go to any directory outside $GOPATH\/src folder. Let&#8217;s say the directory name is <strong>learn<\/strong>.&nbsp;<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">mkdir learn\ncd learn<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Let&#8217;s say the module import path is <strong>sample.com\/learn<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">go mod init sample.com\/learn<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">This command will create a <strong>go.mod<\/strong> file in the same directory.<\/p>\n\n\n\n<p class=\"has-medium-font-size\">Let&#8217;s examine the contents of this file. Do a cat<strong> go.mod<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">module sameple.com\/learn\n\ngo 1.14<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">When the module is first created using the init command, go.mod file will have two things only<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Import path of the module at the top<\/li><\/ul>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">module sameple.com\/learn<\/code><\/pre>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Version of go with which the module was created<\/li><\/ul>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">go 1.14<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Since it is an empty module it doesn&#8217;t have any direct dependency specified yet. Let&#8217;s create a file named <strong>main.go <\/strong>in the same directory with below contents<\/p>\n\n\n\n<p class=\"has-medium-font-size\"><strong>main.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package main\n\nimport (\n\t\"fmt\"\n\t\"strings\"\n\n\t\"github.com\/pborman\/uuid\"\n)\n\nfunc main() {\n\tuuidWithHyphen := uuid.NewRandom()\n\tuuid := strings.Replace(uuidWithHyphen.String(), \"-\", \"\", -1)\n\tfmt.Println(uuid)\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Notice the package declaration in above file<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package main<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">This means that above source file belongs to the <strong>main<\/strong> package. Also Notice that we have imported the dependency in the <strong>main.go<\/strong> as well<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">\"github.com\/pborman\/uuid\"<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Since <strong>main.go<\/strong> file belongs to main package, hence we can create an executable. The executable is always built with the last name in the import path of the module which contains the main package. while running the go install command. In our case the import path of the module is sample.com\/learn and the last name in the import path is learn. Hence executable will be created with name learn when running go install.<\/p>\n\n\n\n<p class=\"has-medium-font-size\">Any of three command can be used to create the executable<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li><strong>&#8216;go install learn&#8217;<\/strong><\/li><li><strong>&#8216;go install&#8217;<\/strong><\/li><li><strong>&#8216;go install .&#8217;<\/strong><\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">The name of the directory would not matter here. The name of the executable will always be the same as the name of the module.&nbsp; All the above commands will create an executable name <strong>learn <\/strong>in the <strong>$GOBIN<\/strong> directory. If the <strong>$GOBIN<\/strong> directory is in your path then you can directory run the executable<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">learn<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Also go install command will download all the dependencies that are required in your source files and update <strong>go.mod<\/strong> file with that dependency. <\/p>\n\n\n\n<p class=\"has-medium-font-size\">After running this command let&#8217;s now let&#8217;s again examine the contents of <strong>go.mod<\/strong> file<\/p>\n\n\n\n<p class=\"has-medium-font-size\">Do a cat<strong> go.mod<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">module learn\n\ngo 1.14\n\nrequire github.com\/pborman\/uuid v1.2.1<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">It lists direct dependency which was specified in the <strong>main.go<\/strong> file along with exact version of the dependency as well. Now let&#8217;s check the <strong>go.sum<\/strong> file as well.<\/p>\n\n\n\n<p class=\"has-medium-font-size\">Do a cat<strong> go.sum<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">github.com\/google\/uuid v1.0.0 h1:b4Gk+7WdP\/d3HZH8EJsZpvV7EtDOgaZLtnaNGIu1adA=\ngithub.com\/google\/uuid v1.0.0\/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw\/LqOeaOT+nhxU+yHo=\ngithub.com\/pborman\/uuid v1.2.1 h1:+ZZIw58t\/ozdjRaXh\/3awHfmWRbzYxJoAdNJxe\/3pvw=\ngithub.com\/pborman\/uuid v1.2.1\/go.mod h1:X\/NO0urCmaxf9VXbdlT7C2Yzkj2IKimNn4k+gtPdI\/k=<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>go.sum<\/strong> file lists down the checksum of direct and indirect dependency required by the module.&nbsp; <a href=\"http:\/\/github.com\">github.com<\/a>\/google\/uuid is internally used by the <a href=\"http:\/\/github.com\">github.com<\/a>\/pborman\/uuid . It is an indirect dependency of the module and hence it is recorded in the <strong>go.sum<\/strong> file. Both the direct dependency as well as the indirect dependency will be downloaded in the $GOAPTH\/pkg\/mod\/cache folder with versioning.<\/p>\n\n\n\n<p class=\"has-medium-font-size\">We can also run the executable directly.<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">learn<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Note: <strong>$GOBIN<\/strong> directly needs to be in your path for above command to run.<\/p>\n\n\n\n<p class=\"has-medium-font-size\"><strong>Output<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">e594dc4d9a754bcb83b56e89b18b4b46<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">The above way we added a dependency in the source file and when we run go install it downloaded that dependency and added it in the go.mod file.&nbsp; Also the executable got created in the <strong>$GOBIN<\/strong> directory.<\/p>\n\n\n\n<p class=\"has-medium-font-size\">Now couple of points to notice<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Name of the directory is <strong>learn<\/strong><\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">Name of the directory which contains the <strong>go.mod<\/strong> file doesn&#8217;t matter. You can try changing name to anything. It will always create the executable with the same name as last part in module import path.<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Import path of the module is <strong>sample.com\/learn<\/strong><\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">The executable is always created with the name of the last part in the module import path which is <strong>learn<\/strong> here. How does import path matter we will learn in the second part of the tutorial. For now, just understand that the module import path is used to import that module into another module. Also if the module import path is just one name then executable will be created with that name only. For example, it is possible that the module import path would only have been just <strong>learn. <\/strong>In this case, too executable would have been created with name learn only. So for the below module import paths executable name would be <strong>learn<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">sample.com\/manage\/learn\nsample.com\/learn\nlearn<\/code><\/pre>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Name of file is <strong>main.go<\/strong><\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">The name of the file won&#8217;t matter here when running &#8216;go install&#8217;. You can try changing the file from main.go to test.go. After doing that run the above commands again. It will create an executable with the module name which is <strong>learn <\/strong>and nothing changes.<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Name of package in learn module is <strong>main<\/strong><\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">The name of the package does matter. If go install sees a main package in the directory, it will create an executable in the <strong>$GOBIN<\/strong> directory. The name of the executable will be the same as the last name in the module import path.<\/p>\n\n\n\n<p class=\"has-medium-font-size\">What we learnt so far:<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Only <strong>main<\/strong> package is executable.<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>The name of the directory containing the module doesn&#8217;t play any role in the name of the executable.<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>On running <strong>&#8216;go install<\/strong>&#8216; it creates the binary with the name as the last part of the module import that contains the .go file belonging to the main package.<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>The name of the file doesn&#8217;t matter when running go install. You can have any name<\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">Let&#8217;s also see the same example before modules to understand the benefits offered with the introduction of the module.<\/p>\n\n\n\n<h1 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Creating_an_application_before_Module\"><\/span><strong>Creating an application before Module<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<p class=\"has-medium-font-size\">Before module all your code should lie in the <strong>$GOPATH\/src<\/strong> folder. Let&#8217;s create a directory <strong>learn<\/strong> inside <strong>$GOPATH\/src <\/strong>directory.<\/p>\n\n\n\n<p class=\"has-medium-font-size\"><strong>$GOPATH\/src\/learn\/main.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package main\n\nimport (\n\t\"fmt\"\n\t\"strings\"\n\n\t\"github.com\/pborman\/uuid\"\n)\n\nfunc main() {\n\tuuidWithHyphen := uuid.NewRandom()\n\tuuid := strings.Replace(uuidWithHyphen.String(), \"-\", \"\", -1)\n\tfmt.Println(uuid)\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Run<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">export GO111MODULE=off\ngo install<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Before modules the executable is always build with the name of the directory which contains the <strong>main<\/strong> package while running the go install command. In our case the name of directory is <strong>learn<\/strong><\/p>\n\n\n\n<p class=\"has-medium-font-size\">All the above commands will create an executable name <strong>learn <\/strong>in the $GOBIN directory. If the $GOBIN directory is in your path then you can directory run the executable<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">learn<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Let&#8217;s see the limitations before modules<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>All code needs to reside in the <strong>$GOPATH\/src\/ <\/strong>folder<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>When you do a go install, it will download both direct and indirect dependency in the <strong>$GOPATH\/src<\/strong> folder without any versioning information.&nbsp; You can check your&nbsp; <strong>$GOPATH\/src <\/strong>folder. It would have downloaded the <strong>&#8220;github.com\/pborman\/uuid&#8221;<\/strong> dependency without any versioning<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>There is no way to define the dependency version within code. A simple go get will download the latest version of the dependency and save it at location <strong>$GOPATH\/src <\/strong>overriding the previous version if already present.<\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">Modules solve all this problem as we have seen in the first example. Now we have understood the basics of packages and modules and what advantages do modules provide. Let&#8217;s now focus only on understanding the package more in detail here in this tutorial. We will focus more on modules in the second part of this tutorial- modules. Here is the link for second part &#8211; <a href=\"https:\/\/golangbyexamples.com\/packages-modules-go-second\">https:\/\/golangbyexamples.com\/packages-modules-go-second<\/a>\/<\/p>\n\n\n\n<p class=\"has-medium-font-size\">Let&#8217;s now add another file belonging to the main package.<\/p>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/subtract.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package main\nfunc subtract(a, b int) int {\n    return a - b\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/main.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package main\nimport \"fmt\"\nfunc main() {\n    fmt.Println(add(2, 1))\n    fmt.Println(subtract(2, 1))\n}\nfunc add(a, b int) int {\n    return a + b\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Try running the go install command again. It will create an executable with name <strong>learn<\/strong> in the <strong>$GOBIN<\/strong> directory. Try running this executable ,It will give below output. Also notice function <strong>main<\/strong> in <strong>main.go<\/strong> is able to call the function <strong>subtract<\/strong> in <strong>subtract.go<\/strong>. It is possible because both <strong>main<\/strong> and <strong>subtract<\/strong> belong to same package main.<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">learn $ learn\n3\n-1<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">So basically<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Within the same package, all variables, functions, constants are accessible between different .go files belonging to the package.<\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">All <strong>.go<\/strong> files present in the same directory will belong to the same package. This is true for all directory containing packages. It doesn&#8217;t matter whether that directory contains the <strong>go.mod<\/strong> file or not. &nbsp; Let&#8217;s validate that. Change the package declaration to<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package subtract<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>go.mod<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">module sameple.com\/learn\n\ngo 1.14<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/subtract.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package subtract\n\nfunc subtract(a, b int) int {\n    return a-b\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/main.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package main\n\nimport \"fmt\"\n\nfunc main() {\n    fmt.Println(add(2, 1))\n    fmt.Println(subtract(2, 1))\n}\n\nfunc add(a, b int) int {\n    return a + b\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Notice the <strong>Package Declaration. <\/strong>It is<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package subtract<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Let&#8217;s try running the <strong>go install <\/strong>command. It will give error<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">can't load package: package learn: found packages subtract (subtract.go) and main (main.go) in<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">The above error means that directory <strong>learn<\/strong> contains two files <strong>subtract.go<\/strong> and <strong>main.go<\/strong> belonging to two different packages named <strong>subtract<\/strong> and <strong>main <\/strong>respectively.&nbsp; GO source files belonging to different packages with in the same directory is not allowed hence this error. Change the <strong>Package Declaration<\/strong> in subtract.go to belong to <strong>main<\/strong> package and the error will go away<\/p>\n\n\n\n<p class=\"has-medium-font-size\">As you might have noticed we are using two functions, <strong>add<\/strong> and <strong>subtract. <\/strong>These two methods are arithmetic functions and it will be good if we can make as part of&nbsp;some common code which can be used by other parts. This is where package is useful . Idea is to create a new package <strong>math <\/strong>which will include these two functions.&nbsp; Through this way package provides a way of code reusability. Let&#8217;s introduce a new package <strong>math<\/strong><\/p>\n\n\n\n<p class=\"has-medium-font-size\"><strong>go.mod<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">module sameple.com\/learn\n\ngo 1.14<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/math\/math.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package math\n\nfunc Add(a, b int) int {\n    return a + b\n}\nfunc Subtract(a, b int) int {\n    return a - b\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/main.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package main\n\nimport (\n    \"fmt\"\n    \"sample.com\/learn\/math\"\n)\n\nfunc main() {\n    fmt.Println(math.Add(2, 1))\n    fmt.Println(math.Subtract(2, 1))\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">If you run this program, output will be same:<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">3\n1<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Couple of points to notice about above program<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li><strong>Importing of a package<\/strong><\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">main.go file imports the package using <strong>&#8220;sample.com\/learn\/math&#8221; <\/strong>and is able to call Add and Subtract using math.Add(..) and math.Subtract(..)See how we have imported the math package in the main.go file.<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">\"sample.com\/learn\/math\"<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Here the import path is import path of module which is <strong>learn<\/strong> +&nbsp; directory containing the package which is <strong>math. <\/strong>Hence <strong>&#8220;sample.com\/learn\/math&#8221;<\/strong> . Packages in nested directory can also be imported in the same way.<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li><strong>Creation of a package<\/strong><\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">We created new directory math and created new file math.go in it. The math.go has Package Declaration as &#8220;package math&#8221;. It also has file <strong>math.go<\/strong> which contains two functions <strong>Add<\/strong> and <strong>Subtract<\/strong>.<\/p>\n\n\n\n<p class=\"has-medium-font-size\">Let&#8217;s talk about the import statement first. There are two ways in which we can import a package<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>A short hand for import<\/li><\/ul>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">import (\n    \"fmt\"\n    \"sample.com\/learn\/math\"\n)<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">and another form<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">import \"fmt\"\nimport \"sample.com\/learn\/math\"<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">You can import any number of packages in a program. GO tries to resolve in below way<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Check at directory $GOROOT\/src &#8211; &#8220;fmt&#8221; package lies at location <strong>$GOROOT\/src\/fmt<\/strong><\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>With modules, it resolves the path starting from the root of the module i.e, the directory which contains the <strong>go.mod<\/strong> file.<\/li><\/ul>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">import \"sample.com\/learn\/math\"<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Above statement essentially means that import package present at location <strong>&#8220;sample.com\/learn\/math&#8221;. <\/strong>It doesn&#8217;t mean import package <strong>math<\/strong>. To validate that let&#8217;s change the directory name to <strong>math2. Package Declaration <\/strong>is still same which is<strong> &#8220;package math&#8221;<\/strong><\/p>\n\n\n\n<p class=\"has-medium-font-size\"><strong>go.mod<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">module sample.com\/learn\n\ngo 1.14<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/math2\/math.go &#8211; <\/strong>Notice that directory name is <strong>math2<\/strong> here<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package math\n\nfunc Add(a, b int) int {\n    return a + b\n}\n\nfunc Subtract(a, b int) int {\n    return a - b\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/main.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package main\n\nimport (\n    \"fmt\"\n    \"sample.com\/learn\/math2\"\n)\n\nfunc main() {\n    fmt.Println(math.Add(2, 1))\n    fmt.Println(math.Subtract(2, 1))\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">If you run this program, output will still be same:<\/p>\n\n\n\n<p class=\"has-medium-font-size\">In <strong>main.go<\/strong> the import folder changes to <strong>&#8220;sample.com\/learn\/math2&#8221;<\/strong> but it&nbsp; <strong>main<\/strong> function in <strong>main.go<\/strong> still refers to <strong>Add<\/strong> and <strong>Subtract<\/strong> as <strong>math.Add()<\/strong> and <strong>math.Subtract() <\/strong>. So basically GO imports <strong>math<\/strong> package from <strong>&#8220;math2&#8221; <\/strong>directory. This is what we meant when we said&nbsp; import means to import package present at that directory location.<\/p>\n\n\n\n<p class=\"has-medium-font-size\">So we now know&nbsp; the use of a package directory name<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Use of the directory is for import statements in GO program. In import, we provide the directory path and not the package name. GO then fetches all the files having the same package name.<\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">What about filename. In above case filename is <strong>math.go. <\/strong>Filename doesn&#8217;t matter. You can try changing filename from <strong>math.go<\/strong> to something else. Output will still the same.<\/p>\n\n\n\n<p class=\"has-medium-font-size\">Let&#8217;s move ahead. You might have noticed that both <strong>Add<\/strong> and <strong>Subtract<\/strong> are capitalized. Why is that. What will happen if they are not capitalized. If Add and Subtract were not capitalized, then <strong>main.go<\/strong> won&#8217;t be able to refer them. This brings our next topic for discussion.<\/p>\n\n\n\n<h1 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Exported_vs_Unexported_Names\"><\/span><strong>Exported vs Unexported Names<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<p class=\"has-medium-font-size\">Go doesn&#8217;t have any <strong>public<\/strong>,&nbsp; <strong>private<\/strong> or <strong>protected<\/strong> keyword. The only mechanism to control the visibility is using the capitalized and non-capitalized formats<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li><strong>Capitalized Identifiers<\/strong> are exported. The capital letter indicates that this is an exported identifier. It will be visible in other packages&nbsp;<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li><strong>Non-capitalized identifiers <\/strong>are not exported.&nbsp;The lowercase indicates that the identifier is not exported and will only be accessed from within the same package.<\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">There are five kinds of identifier which can be exported or non-exported<\/p>\n\n\n\n<ol class=\"has-medium-font-size wp-block-list\"><li>Structure<\/li><li>Structure&#8217;s Method<\/li><li>Structure&#8217;s Field<\/li><li>Function<\/li><li>Variable<\/li><\/ol>\n\n\n\n<p class=\"has-medium-font-size\">Let&#8217;s add a function named <strong>multiply <\/strong>which will be in lowercase. We will add it to math package and see if it is accessible from <strong>main.go<\/strong>.<\/p>\n\n\n\n<p class=\"has-medium-font-size\"><strong>go.mod<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">module sameple.com\/learn\n\ngo 1.14<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/math\/math.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package math\nfunc Add(a, b int) int {\n    return a + b\n}\nfunc Subtract(a, b int) int {\n    return a - b\n}\nfunc multiply(a, b int) int {\n    return a * b\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/main.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package main\nimport (\n    \"fmt\"\n    \"sample.com\/learn\/math\"\n)\nfunc main() {\n    fmt.Println(math.Add(2, 1))\n    fmt.Println(math.Subtract(2, 1))\n    fmt.Println(math.multiply(2, 1))\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Let&#8217;s run this program. It will give error<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">learn $ go install\nlearn $ learn\n.\/main.go:12:14: cannot refer to unexported name math.multiply\n.\/main.go:12:14: undefined: math.multiply<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">The error is because <strong>main.go<\/strong> cannot refer to unexported name <strong>math.multiply<\/strong>. Make multiply as uppercase and it will work. It should give below output after that.<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">3\n1\n2<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Also as mentioned during the start of the tutorial, <strong>multiply<\/strong> function will be available within the <strong>math<\/strong> package. To illustrate this let&#8217;s create a function <strong>Mul <\/strong>in arithmetic.go which will call <strong>multiply<\/strong> function internally<\/p>\n\n\n\n<p class=\"has-medium-font-size\"><strong>go.mod<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">module sameple.com\/learn\n\ngo 1.14<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/math\/math.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package math\nfunc Add(a, b int) int {\n    return a + b\n}\nfunc Subtract(a, b int) int {\n    return a - b\n}\nfunc Mul(a, b int) int {\n    return multiply(a, b)\n}\nfunc multiply(a, b int) int {\n    return a * b\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/main.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package main\nimport (\n    \"fmt\"\n    \"sample.com\/learn\/math\"\n)\nfunc main() {\n    fmt.Println(math.Add(2, 1))\n    fmt.Println(math.Subtract(2, 1))\n    fmt.Println(math.Mul(2, 1))\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Let&#8217;s run this program<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">learn $ go install\nlearn $ learn\n3\n1\n2<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">The above program works because within the same package you can refer to unexported or non-capitalized names as well.<\/p>\n\n\n\n<p class=\"has-medium-font-size\">For now <strong>math.go<\/strong> contains both <strong>Add<\/strong> and <strong>Subtract<\/strong> function. Can we distribute these two functions to different files with these function still belonging to same package <strong>math. <\/strong>Yes we can do that. Let&#8217;s create <strong>add.go<\/strong> and <strong>subtract.go<\/strong> file inside the <strong>math<\/strong> directory. add.go will contain the <strong>Add<\/strong> function and subtract.go will contain the <strong>Subtract<\/strong> function. Notice that both <strong>add.go<\/strong> and <strong>subtract.go<\/strong> have the same package declaration which is <strong>package math<\/strong><\/p>\n\n\n\n<p class=\"has-medium-font-size\"><strong>go.mod<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">module sameple.com\/learn\n\ngo 1.14<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/math\/add.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package math\nfunc Add(a, b int) int {\n    return a + b\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/math\/subtract.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package math\nfunc Subtract(a, b int) int {\n    return a - b\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/main.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package main\nimport (\n    \"fmt\"\n    \"sample.com\/learn\/math\"\n)\nfunc main() {\n    fmt.Println(math.Add(2, 1))\n    fmt.Println(math.Subtract(2, 1))\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Let&#8217;s run this program<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">learn $ go install\nlearn $ learn\n3\n1<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">It works because the import statement in <strong>main.go<\/strong> fetches all identifiers from all files which belong to package <strong>math<\/strong> from import. path <strong>&#8220;sample.com\/learn\/math&#8221;<\/strong><\/p>\n\n\n\n<h1 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Nested_Packages\"><\/span><strong>Nested Packages<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<p class=\"has-medium-font-size\">In GO it is possible to create nested packages. Let&#8217;s create a new directory named <strong>advanced<\/strong> inside <strong>math<\/strong> directory.&nbsp; &#8220;<strong>. <\/strong>This directory will contain <strong>square<\/strong>.go file which will package declaration as<strong> &#8220;package advanced&#8221;<\/strong><\/p>\n\n\n\n<p class=\"has-medium-font-size\"><strong>go.mod<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">module sameple.com\/learn\n\ngo 1.14<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/math\/math.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package math\nfunc Add(a, b int) int {\n    return a + b\n}\nfunc Subtract(a, b int) int {\n    return a - b\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/math\/advanced\/advanced.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package advanced\nfunc Square(a int) int {\n    return a * a\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/main.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package main\nimport (\n    \"fmt\"\n    \"sample.com\/learn\/math\"\n    \"sample.com\/learn\/math\/advanced\"\n)\nfunc main() {\n    fmt.Println(math.Add(2, 1))\n    fmt.Println(math.Subtract(2, 1))\n    fmt.Println(advanced.Square(2))\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Let&#8217;s run this program<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">learn $ go install\nlearn $ learn\n3\n1\n4<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Points to note about above program<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>We imported the <strong>advanced<\/strong> package in main.go with full qualified path i.e,&nbsp; <strong>import &#8220;sample.com\/learn\/math\/advanced&#8221;<\/strong><\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li><strong>Square<\/strong> function is referred using <strong>advanced<\/strong> package i.e, <strong>advanced.Square(2)<\/strong><\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>As mentioned earlier directory name can be other <strong>advanced<\/strong> just that it has to be imported accordingly<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Also filename can be anything other than <strong>advanced.go<\/strong><\/li><\/ul>\n\n\n\n<h1 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Aliasing_in_importing_packages\"><\/span><strong>Aliasing in importing packages<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<p class=\"has-medium-font-size\">Aliasing in importing packages means give a different name to the imported package. Syntax for it is<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">import <new_name> <directory_path><\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Above statement means that what ever package is present at directory &lt;directory_path&gt; import that package with name &lt;new_name&gt;. Aliasing is useful for giving<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Giving more relevant name to the imported package in the current context.<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>When two different import path contains same package name then import one of them as a different name to prevent conflict.<\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">Let&#8217;s see an example.<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Create a folder <strong>math2. <\/strong>Create a file <strong>math2.go <\/strong>with the below contents having the <strong>Subtract<\/strong> function. Package Declaration in <strong>math2.go<\/strong> is &#8220;package math&#8221; which means the package name is still <strong>math<\/strong><\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li><strong>math <\/strong>folder still contains <strong>math.go <\/strong>file with the only <strong>Add<\/strong> function<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Notice that package name (i.e <strong>math<\/strong>) is same in folder <strong>math<\/strong> as well in folder <strong>math2. <\/strong>So both folder <strong>math2<\/strong> and <strong>math<\/strong> contains the same package which is <strong>math<\/strong><\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\"><strong>go.mod<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">module sameple.com\/learn\n\ngo 1.14<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/math2\/math2.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package math\nfunc Subtract(a, b int) int {\n    return a - b\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/math\/math.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package math\nfunc Add(a, b int) int {\n    return a + b\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/main.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package main\nimport (\n    \"fmt\"\n    \"sample.com\/learn\/math\"\n    math2 \"sample.com\/learn\/math2\"\n)\nfunc main() {\n    fmt.Println(math.Add(2, 1))\n    fmt.Println(math2.Subtract(2, 1))\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Let&#8217;s run this program<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">go install\nlearn $ learn\n3\n1<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Notice the line. We alias <strong>math<\/strong> package present <strong>&#8220;sample.com\/learn\/math2&#8221;<\/strong> to <strong>math2. <\/strong>If we haven&#8217;t done that then GO will raise a compilation issue as it cannot import package with same name from two different folders. This one of the advantage of using alias.<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">math2 \"sample.com\/learn\/math2\"<\/code><\/pre>\n\n\n\n<h1 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Init_Functions\"><\/span><strong>Init Functions<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<p class=\"has-medium-font-size\">init() function is a special function that is used to initialize global variables of a package. These functions are executed when the package is initialized. Each of the GO source files in a package can have its own init() function. Whenever you import any package in the program, then on the execution of that program, init functions(if present)&nbsp; in the GO source files belonging to that imported package are called first. Some points to note about init function<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Init function is optional<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Init function does not take any argument<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Init function does not have any return value.<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Init function is called implicitly. Since it is called implicitly, init function cannot reference it from anywhere.<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>There can be multiple init() functions within the same source file.<\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">init function is majorly used for the initialization of global variables that cannot be initialized using an initialization expression. For example, it requires a network call to intialize any DB client. Another example could be fetching secret keys on startup. Init function is also used for running anything that only needs to be executed once. Let&#8217;s see a simple use case of using an init function.&nbsp;<\/p>\n\n\n\n<p class=\"has-medium-font-size\">Let&#8217;s see an example of using an init function.<\/p>\n\n\n\n<p class=\"has-medium-font-size\"><strong>go.mod<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">module sameple.com\/learn\n\ngo 1.14<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/math\/add.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package math\n\nimport \"fmt\"\n\nfunc init(){\n\tfmt.Println(\"In add init\")\n}\n\nfunc Add(a, b int) int {\n\treturn a + b\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/math\/subtract.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package math\n\nimport \"fmt\"\n\nfunc init(){\n\tfmt.Println(\"In subtract init\")\n}\n\nfunc Subtract(a, b int) int {\n\treturn a - b\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/main.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package main\n\nimport (\n\t\"fmt\"\n\n\t\"sample.com\/learn\/math\"\n)\n\nfunc init(){\n    fmt.Println(\"In main init\")\n}\n\nfunc main() {\n\tfmt.Println(math.Add(2, 1))\n\tfmt.Println(math.Subtract(2, 1))\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>Output<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">In add init\nIn subtract init\nIn main init\n3\n1<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Notice from the output that<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>init() function in the math\/add.go file is executed and it prints &#8211; &#8220;In add init&#8221;<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>init() function in the math\/subtract.go file is executed next and it prints &#8211; &#8220;In subtract init&#8221;<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>init() function in the main.go file is executed next and it prints &#8211; &#8220;In main init&#8221;<\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">Although both the source files belong to the same package math but init function in both the source files gets executed.<\/p>\n\n\n\n<h1 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Order_of_execution_of_a_Go_program\"><\/span><strong>Order of execution of a Go program<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<p class=\"has-medium-font-size\">Below the order of execution of a go program.<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>The program starts with the main package.<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>All imported packages in the source files of the main package are initialized. The same thing happens recursively for further imported packages.<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Then global variables declaration in these packages is initialized. The initialization dependency kicks in for the initialization of these variables. <a href=\"https:\/\/golang.org\/ref\/spec#Order_of_evaluation\">https:\/\/golang.org\/ref\/spec#Order_of_evaluation<\/a><\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>After this, init() function is run in these packages<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Global variables in the main package are initialized<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>init function in the main package is run if present<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>main function in main package is run.<\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">Note here that package initialization is only done once even if it is imported several times.&nbsp;<\/p>\n\n\n\n<p class=\"has-medium-font-size\">For example, if the main package imports package <strong>a<\/strong> and in turn package <strong>a<\/strong> imports package <strong>b<\/strong>, then below will be the order<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Global variables in package <strong>b<\/strong> will be initialized. <strong>init<\/strong> function in source files of package <strong>b<\/strong> will be run<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Global variables in the package <strong>a<\/strong> will be initialized. <strong>init<\/strong> function in source files of package b will be run<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Global variables in the <strong>main<\/strong> package will be initialized. init function in source files of the <strong>main<\/strong> package will be run<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>The <strong>main<\/strong> function will start executing.<\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">Let&#8217;s see a program for the same.<\/p>\n\n\n\n<p class=\"has-medium-font-size\"><strong>go.mod<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">module sameple.com\/learn\n\ngo 1.14<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/b\/b1.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package b\n\nimport (\n\t\"fmt\"\n)\n\nfunc init() {\n\tfmt.Println(\"Init: b1\")\n}\n\nfunc TestB() error {\n\treturn nil\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/b\/b2.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package b\n\nimport (\n\t\"fmt\"\n)\n\nfunc init() {\n\tfmt.Println(\"Init: b2\")\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/a\/a1.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package a\n\nimport (\n\t\"fmt\"\n\t\"sample\/b\"\n)\n\nfunc init() {\n\tfmt.Println(\"Init: a1\")\n}\n\nfunc TestA() error {\n\treturn b.TestB()\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/a\/a2.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package a\n\nimport (\n\t\"fmt\"\n)\n\nfunc init() {\n\tfmt.Println(\"Init: a2\")\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>learn\/main.go<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">package main\n\nimport (\n\t\"fmt\"\n\t\"sample\/a\"\n)\n\nfunc init() {\n\tfmt.Println(\"Init: main\")\n}\nfunc main() {\n\tfmt.Println(\"Main Function Executing\")\n\ta.TestA()\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\"><strong>Output<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">Init: b1\nInit: b2\nInit: a1\nInit: a2\nInit: main\nMain Function Executing<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Notice in the above example that the <strong>init<\/strong> function in source files of package <strong>b<\/strong> is run first. Then <strong>init<\/strong> function in source files of the package <strong>a<\/strong> is run and then <strong>init<\/strong> function in the source file of the main package is run. After that <strong>main<\/strong> function is run<\/p>\n\n\n\n<h1 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Blank_Identifier_in_import\"><\/span><strong>Blank Identifier in import<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<p class=\"has-medium-font-size\">Blank identifier in importing packages means specifying a blank import for the imported package. The syntax for it is<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">import _ <directory_path><\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">What is this blank import and why it is used. For this, you have to understand two things<\/p>\n\n\n\n<ol class=\"has-medium-font-size wp-block-list\"><li>About <strong>init<\/strong> function<\/li><li>About blank identifier represented by an underscore (&#8216;<strong>_<\/strong>&#8216;)<\/li><\/ol>\n\n\n\n<p class=\"has-medium-font-size\"><strong>init()<\/strong> function we already studied above.<\/p>\n\n\n\n<p class=\"has-medium-font-size\">Now let&#8217;s come to blank identifier.<\/p>\n\n\n\n<p class=\"has-medium-font-size\">You are already aware that go doesn&#8217;t allow any unused variable. Any unused variable can be replaced by a blank identifier (&#8216;_&#8217;).<br>So now a blank import of a package is used when<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>The imported package is not being used in the current program<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>But we intend to import that package so that the <strong>init<\/strong> function in the GO source files belonging to that package can be called and initialization of variables in that package can be done properly<\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">So basically a blank import is used when a package is solely imported for its side effects. As an example MySQL package is used as a blank import for its side-effect of registering the&nbsp;MySQL&nbsp;driver as a database driver in the&nbsp;<strong>init()<\/strong> function of MySQL package, without importing any other functions:<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">_ \"github.com\/go-sql-driver\/mysql\"<\/code><\/pre>\n\n\n\n<h1 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Package_Naming_Convention\"><\/span><strong>Package Naming Convention<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<p class=\"has-medium-font-size\">A good name is very important for the package as any access to the package&#8217;s types, functions, constants, or variables is prefixed by the package name. So the package name should be short and clear. It is recommended to avoid<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Underscore in the package name<\/li><li>Camel casing or any kind of mixed caps<\/li><\/ul>\n\n\n\n<h1 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Conclusion\"><\/span><strong>Conclusion<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<p class=\"has-medium-font-size\">In this tutorial, we learned about packages and gave a small introduction to modules. It is important to understand packages first before we can jump fully to modules. In the second part of this tutorial, we will focus entirely on modules. Hope you have liked this article. Please share feedback\/mistakes\/improvements in the comments<\/p>\n\n\n\n<p class=\"has-medium-font-size\"><strong><strong>Next Tutorial<\/strong> &#8211; <\/strong><a href=\"https:\/\/golangbyexamples.com\/packages-modules-go-second\/\">Packages and Modules &#8211; Part 2<\/a><strong><br><strong>Previous Tutorial<\/strong> &#8211; <\/strong><a href=\"https:\/\/golangbyexamples.com\/workspace-hello-world-golang\/\">Set up GO Workspace and Hello World Program<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>This is the chapter 4 of the golang comprehensive tutorial series. Refer to this link for other chapters of the series &#8211; Golang Comprehensive Tutorial Series Next Tutorial &#8211; Packages and Modules&#8230;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"spay_email":"","footnotes":"","jetpack_publicize_message":"","jetpack_is_tweetstorm":false},"categories":[1],"tags":[3,4],"class_list":["post-4348","post","type-post","status-publish","format-standard","hentry","category-tech","tag-go","tag-golang"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v22.7 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Packages and Modules in Go (Golang) - Part 1 - Welcome To Golang By Example<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/golangbyexamples.com\/packages-modules-go-first\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Packages and Modules in Go (Golang) - Part 1 - Welcome To Golang By Example\" \/>\n<meta property=\"og:description\" content=\"This is the chapter 4 of the golang comprehensive tutorial series. 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