go:generate 101

How to use go:generate?

support code

Setup

terminal

go mod init github.com/<username>/<reponame>

Create two files. main.go will use gen.go as generator.

terminal

touch main.go gen.go

main.go simply logs "World!" and runs the generator via the special comment.

main.go

package main

//go:generate go run gen.go

import "fmt"

func init() {
    fmt.Println("main.go#main.init")
}

func main() {
    fmt.Println("World!")
}

NOTE: There is no space between the slashes and go:generate.

NOTE: not only gen.go, but go run gen.go.

gen.go declares package main, which would be forbidden were it not for the special comment.

gen.go

//go:build ignore

package main

import "fmt"

func init() {
    fmt.Println("gen.go#main.init")
}

func main() {
    fmt.Println("Hello")
}

NOTE: There is not space between the slashes and go:build.

Usage

terminal

go generate ./...

Output

gen.go#main.init
Hello

terminal

go run .

terminal

main.go#main.init
World!

Although the subcommand name is generate, the **generator* need not generate a file.*

References

• support code