array of functions/delegates

[Mike Parker]

On Tuesday, 24 December 2019 at 07:37:02 UTC, Rumbu wrote:
> I am trying to create an array of functions inside a struct.
>
> struct S {
>   void f1() {}
>   void f2() {}
>
>   alias Func = void function();
>
>  immutable Func[2] = [&f1, &f2]
>
> }
>
> What I got: Error: non-constant expression '&f1'
>
> Tried also with delegates (since I am in a struct context but I 
> got: no `this` to create delegate `f1`.
>
> So, is there any way to have an array of functions without 
> adding them at runtime?

This isn't an array of functions you're creating here. A pointer 
to a member function is *always* a delegate, unless the function 
is static. Pointers to functions can be known at compile time, so 
this works:


struct S () {
     static void f1() {}
     static void f2() {}

     alias Func = void function();

     immutable Func[2] funcs = [&f1, &f2];

}

As does this:

struct S {}
void f1(S s) {}
void f2(S s) {}

alias Func = immutable(void function());

immutable Func[2] funcs = [cast(Func)&f1, cast(Func)&f2];

Though, it's not clear to me wy the one requires casting the 
pointer type and the other doesn't.