Go Modules

Links: 103 Golang Index

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Modules

• A module is a collection of Go packages stored in a file tree with a go.mod file at its root.
  • It is like package.json in npm and is used for dependency management.
  • We can use different versions of the same dependency.
• Basic structure of the go.mod file

  module <name>
  go <version>
  require <module-path> <version>
  

• go mod init name to initialise a go module
  • Typically its host hosting the code/user or organisation/repo name: github.com/user/repo
• go mod tidy: to add the third party and remove packages from go.mod file as and when you add and remove third party imports from your source files.
• If we want to get some modules we can use go get ...

Module name is the import path prefix for all packages within the module (local packages).

• Go modules that are downloaded are stored locally at $GOPATH/pkg/mod.

  • Also known as module caching to prevent repeated downloads of the module.
  • If you are downloading files from github then they will be inside the directory github.com

• We import the package and not the module. So provide the git path to the package.

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  • But the go.mod file will have something like this require github.com/ddadumitrescu/go_math v1.1.0 since we download the full repo.
• If we are doing a go get then we provide the path to the repo.
• Updating the dependencies go get -u: this will only work for minor updates and not patches and major updates.

• //indirect in the go.mod file means no file is using that package.

• We can use different versions of the same package using aliases.

  import (
      packagev1 "github.com/user/repo/package"
      packagev2 "github.com/user/repo/v2/package"
  )
  

A new version of a Go package that you are using in an application was released. How do you update to the new version?

By manually editing go.mod or running go get command.

Sample Project Structure

While importing we are importing by directory name and not the package name. But while using anything inside the source code we are using package name.

• Example
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  • Better to use directory name as the package name

Compiling and Running Programs

• go run main.go is used to compile and run the file. It doesn't create any executable.
• go build creates an executable with the same name as directory inside the directory.
  • If you want to give the executable another option then you use go build -o other_name
  • In a directory that contains many Go source files you run go build. It will compile all the source files in the current directory and will produce an executable with the name of the directory.
• We can compile the executable binary for any OS in any OS using the GOOS and GOARCH parameters.
  • GOOS=linux GOARCH=amd64 go build -o linuxapp
• gofmt is formatting the go files according to a set standard. Eg: gofmt -w main.go here -w means it will overwrite the source file.
  • You can also run it on the whole directory gofmt -w directory_path
  • or you can run go fmt in the parent directory and it will format the code of all the go files.

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Last updated: 2022-06-06