Algebraic data types

[Jonathan via Digitalmars-d]

NM, I found this:
http://www.digitalmars.com/d/archives/digitalmars/D/Algebraic_Data_Types_in_D_239039.html

"D's Algebraic needs some work, but it's okay for basic usage." 
+1 agree
----

import std.stdio;
import std.variant;

struct Red {}
struct Green{}
struct Blue {}
struct RGB
{
	int r;
	int g;
	int b;
}

alias Color = Algebraic!(Red, Green, Blue, RGB);

void main()
{
	auto r = Color(RGB(64, 128, 255));
	r.visit!(
		(Red   r) => writeln("Red"),
		(Green g) => writeln("Green"),
		(Blue  b) => writeln("Blue"),
		(RGB rgb) => writefln("RGB(%s, %s, %s)", rgb.r, rgb.g, rgb.b),
	);
}