How to simulate classes and virtual methods in Golang.

gistfile1.go

/*
	How to simulate classes and virtual methods in Go.
*/

package main

import . "fmt"

type A struct {
	// Set My to outermost object (most derived class) after constructing.
	// To call virtual functions, cast My to an interface containing the method you want.
	My interface{}

	a int
}

func (me *A) F() int {
	return me.My.(VirtA).M() + 1000
}

func (me *A) tryG() int {
	bp, ok := me.My.(VirtB)
	if ok {
		return bp.G()
	}
	return -1 // because conversion failed.
}

func (me *A) M() int {
	return me.a * me.a
}

type B struct {
	A	// embed the "superclass"
	b int
}
func (me* B) super() *A { return &me.A }

func (me *B) G() int {
	return me.My.(VirtA).M() + 2000
}

func (me *B) M() int {
	return me.a * me.a * me.a
}

type C struct {
	B	// embed the "superclass"
}
func (me* C) super() *B { return &me.B }

func (me *C) G() int {
	return me.My.(VirtA).M() + 10 * me.super().G()
}

// For convenience, we define a VirtX interface for each class X.
// We could also define an interface for each method.
type VirtA interface {
	F() int
	M() int
}

type VirtB interface {
	VirtA	// embed the "superclass" interface
	G() int
}

type VirtC interface {
	VirtB	// embed the "superclass" interface
}

func main() {
	var aa *A = &A{nil, 2}
	aa.My = aa  // Set instance of A with A*

	Printf("hello, world\n")
	Printf("aa.F %d\n", aa.F())
	Printf("aa.M %d\n", aa.M())
	Printf("aa.tryG %d\n", aa.tryG())

	var bb *B = &B{A{nil, 2}, 3}
	bb.My = bb  // Set instance of B with B*

	Printf("bb.F %d\n", bb.F())
	Printf("bb.M %d\n", bb.M())
	Printf("bb.tryG %d\n", bb.tryG())

	var cc *C = &C{B{A{nil, 2}, 3}}
	cc.My = cc  // Set instance of C with C*

	Printf("cc.F %d\n", cc.F())
	Printf("cc.M %d\n", cc.M())
	Printf("cc.tryG %d\n", cc.tryG())
}

hello, world
aa.F 1004
aa.M 4
aa.tryG -1
bb.F 1008
bb.M 8
bb.tryG 2008
cc.F 1008
cc.M 8
cc.tryG 20088