patternmatch.d

struct nullable(T){
	T me; alias me this;
	bool isnull=true;
	this(T t){
		me=t;
		isnull=false;
}}
template match(A...){
	auto match(T...)(T args){
		static foreach(f;A[0..$-1]){ {
			auto o=f(args);
			if(! o.isnull){return o.me;}
		}}
		return A[$-1](args);
	}
}
unittest{
	import std;
	alias O=nullable!string;
	O foo(int i){
		if(i%3==0){return O("foo");}
		return O();
	}
	O bar(int i){
		if(i%5==0){return O("bar");}
		return O();
	}
	O foobar(int i){
		if(i%15==0){return O("foobar");}
		return O();
	}
	string litteral(int i){
		return i.to!string;}
	foreach(i;1..100){
		i.match!(foobar,foo,bar,litteral).writeln;
	}
}