go-union

README

go-union

Generates Go code using a package as a union or sum type.

Given the name of a Union type T, go-union will create a new self-contained Go source file implementing

func (m T) Union() any

The file is created in the same package and directory as the package that defines T. It has helpful defaults designed for use with go generate.

For example, given this snippet,

package painkiller

//go:generate go-union -type "Pill"
type Pill[T comparable] struct {
	// This is Name doc comment
	Name      string // This is Name line comment
	Age       string
	Address   string `union:"-"`
	NameAlias string

	arrayType     [5]T
	funcType      func()
	interfaceType interface{}
	mapType       map[string]int
	sliceType     []int64
}

running this command

go-union -type "Pill"

in the same directory will create the file pill_union.go, in package painkiller, containing a definition of

// Code generated by "go-union -type Pill"; DO NOT EDIT.
// Install go-union by \"go get install github.com/searKing/golang/tools/go-union\"

package painkiller

import "reflect"

// Union switch on the variant.
func (u Pill[T]) Union() any {
	if reflect.ValueOf(u.AliasStruct).IsZero() {
		return u.AliasStruct
	}
	{
		var z string
		if u.Name != z {
			return u.Name
		}
	}
	{
		var z int
		if u.Age != z {
			return u.Age
		}
	}
	if reflect.ValueOf(u.NameAlias).IsZero() {
		return u.NameAlias
	}
	if reflect.ValueOf(u.genericFuncType).IsZero() {
		return u.genericFuncType
	}
	if reflect.ValueOf(u.genericStructType).IsZero() {
		return u.genericStructType
	}
	if reflect.ValueOf(u.genericEmptyStructType).IsZero() {
		return u.genericEmptyStructType
	}
	if u.pointerType != nil {
		return u.pointerType
	}
	if reflect.ValueOf(u.structType).IsZero() {
		return u.structType
	}
	{
		var z [5]T
		if u.arrayType != z {
			return u.arrayType
		}
	}
	if u.funcType != nil {
		return u.funcType
	}
	if u.chanType != nil {
		return u.chanType
	}
	{
		var z any
		if u.interfaceType != z {
			return u.interfaceType
		}
	}
	{
		var z string
		if u.stringType != z {
			return u.stringType
		}
	}
	if u.mapType != nil {
		return u.mapType
	}
	if u.indentSliceType != nil {
		return u.indentSliceType
	}
	if u.selectorSliceType != nil {
		return u.selectorSliceType
	}
	if u.starSelectorSliceType != nil {
		return u.starSelectorSliceType
	}
	return nil
}

Typically, this process would be run using go generate, like this:

//go:generate go-union -type "Pill"

If multiple constants have the same value, the lexically first matching name will be used (in the example, Acetaminophen will print as "Paracetamol").

With no arguments, it processes the package in the current directory. Otherwise, the arguments must name a single directory holding a Go package or a set of Go source files that represent a single Go package.

The -type flag accepts a comma-separated list of types so a single run can generate methods for multiple types. The default output file is t_union.go, where t is the lower-cased name of the first type listed. It can be overridden with the -output flag.

Download/Install

The easiest way to install is to run go get install github.com/searKing/golang/tools/go-union . You can also manually git clone the repository to $GOPATH/src/github.com/searKing/golang/tools/go-union.

Inspiring projects

• stringer

Documentation

Overview

go-union Generates Go code using a package as a union or sum type. Given the name of a Union type T, go-union will create a new self-contained Go source file implementing

func (m T) Union() any

The file is created in the same package and directory as the package that defines T. It has helpful defaults designed for use with go generate.

For example, given this snippet,

running this command

go-union -type=Pill

in the same directory will create the file pill_union.go, in package painkiller, containing a definition of

func (u Pill[T]) Union() any

Typically this process would be run using go generate, like this:

//go:generate go-union -type=Pill

With no arguments, it processes the package in the current directory. Otherwise, the arguments must name a single directory holding a Go package or a set of Go source files that represent a single Go package.

The -type flag accepts a comma-separated list of types so a single run can generate methods for multiple types. The default output file is t_string.go, where t is the lower-cased name of the first type listed. It can be overridden with the -output flag.