A function which receives the index and lazy arguments, and returns one of the arguments at the index.

choose.d

import std.stdio;

/// won't compile.
auto choose(T)(size_t i, lazy T[] choice...)
{
	return choice[i];
}

/// to be generalized.
auto choose(T)(size_t i, lazy T c0, lazy T c1)
{
	return i ? c1 : c0;
}

auto arg(T)(T x)
{
	"evaluated %d".writefln(x);
	return x;
}

/// expecting exactly two lines of stdout.
void main()
{
	"chose %d".writefln(choose(2, arg(0), arg(1), arg(2)));
}