import std.typetuple;
alias TL = TypeTuple!(int, double);

int foo(TL td)  // same as int foo(int, double);
{
    return td[0] + cast(int) td[1];
}
assert(foo(1, 2.5) == 3);

alias TL = TypeTuple!(int, double);

alias Types = TypeTuple!(TL, char);
static assert(is(Types == TypeTuple!(int, double, char)));