immutable.go

package main

import (
	"fmt"
	"os"
)

type D struct {
	v string
}

func s(o interface{}) {
	fmt.Fprintf(os.Stdout, "%#v %p\n", o, o)
}

// value in, value out
func alter(d D) D {
	d.v += "-altered"
	return d
}

// pointer in, pointer out
func alterp(d *D) *D {
	d.v += "-altered"
	return d
}

// pointer in, value out
func alterprv(d *D) D {
	d.v += "-altered"
	return *d
}

func main() {
	d := D{"1"}

	s(alter(d))
	s(d)
	s(alterp(&d))
	s(d)
	s(alterprv(&d))
	s(d)

	dp := &D{"2"}

	s(alter(*dp))
	s(dp)
	s(alterp(dp))
	s(dp)
	s(alterprv(dp))
	s(dp)

	dc := *dp
	s(alterp(&dc))
	s(dc)
	s(dp)
}