functionEitherLeft

static real lreal(int x)
{
	import std.math;
	return PI * x;
}
static string rstring(int x)
{
	import std.conv;
	return x.to!string;
}
auto fl = RealFunction!lreal.get.functionEitherLeft!string;
auto fr = RealFunction!rstring.get.functionEitherRight!real;
static assert (is (typeof (fl) == typeof (fr)));