Generating Go Code – `go generate` & Templates

Code Generation

This lesson explains the main concept clearly with beginner-friendly examples and background so you can learn why the code works.

go generate runs commands specified in source files.

//go:generate stringer -type=Day
type Day int

const (
    Sunday Day = iota
    Monday
    Tuesday
    Wednesday
    Thursday
    Friday
    Saturday
)

Run with:

$ go generate ./...

Using text/template to emit code

import "text/template"

const tmpl = `package {{.Pkg}}

// {{.Name}} holds {{.Desc}}
type {{.Name}} struct { {{range .Fields}}{{.Name}} {{.Type}} ` + "`json:\"{{.JSON}}\"`" + `{{end}} }
`

type field struct { Name, Type, JSON string }

data := struct{ Pkg, Name, Desc string; Fields []field }{ "model", "User", "user data", []field{{"ID","int","id"},{"Name","string","name"}} }

t, _ := template.New("code").Parse(tmpl)
 t.Execute(os.Stdout, data)