indexable range support

[crazymonkyyy]

opend -unittest -main -run foo.d
--- foo.d
import std;
auto indexs(T,int N)(ref T[N] a)=>iota(0,N);
auto iteratebyindex(A)(ref A a){
	alias R=typeof(a.indexs);
	struct range{
		A* a;
		R r;
		auto ref front()=>(*a)[r.front];
		auto ref index()=>r.front;
		void popFront()()=>r.popFront;
		bool empty()=>r.empty;
	}
	return range(&a,a.indexs);
}
auto map(alias F,R)(R r){
	struct Map{
		R r;
		auto ref front()=>F(r.front);
		auto ref index()=>r.index;
		void popFront()()=>r.popFront;
		bool empty()=>r.empty;
	}
	return Map(r);
}
unittest{
	int[5] foo=[1,2,4,3,5];
	foreach(i,e;foo.iteratebyindex.map!(a=>a*2)){
		writeln(i,':',e);
}}

error: expected 1 argument

foreach of a range with 2 arguments should attempt to match i to r.index and e to r.front