I don't know if this is supposed to work, but it's handy:


import std.typecons: Tuple;
void main() {
    alias int function(int, int) Op;
    static void foo(Op o) {}
    foo((a, b) => a + b); // OK
    alias Tuple!(Op) T;
    auto t1 = T((int a, int b) => a + b); // OK
    auto t2 = T((a, b) => a + b); // Error
}


DMD 2.060alpha gives:

temp.d(8): Error: template std.typecons.Tuple!(int function(int, int)).Tuple.__ctor does not match any function template declaration
...\dmd2\src\phobos\std\typecons.d(379): Error: template std.typecons.Tuple!(int function(int, int)).Tuple.__ctor cannot deduce template function from argument types !()(void)