callable type (function/delegate/function pointer) or function symbol. Represented by variadic template of length 1 to accept both types and function symbols.
void foo(int x, ref double y, char[] z) {} alias ParametersOf!(typeof(foo)) Params; static assert (Params.length == 3); static assert (is(Params[0] == int)); static assert (is(Params[1] == double)); static assert (is(Params[2] == char[]));
Evaluates to a compile-time sequence representing the parameters of Callable