A comparison between C++ and D

[John Colvin via Digitalmars-d]

On Wednesday, 9 March 2016 at 20:14:13 UTC, Adam D. Ruppe wrote:
> ---
> import std.stdio;
>
> @nogc int delegate(int) dg;
>
> int helper() @nogc {
> 	int a = 50;
>
> 	struct MyFunctor {
> 		int a;
>
> 		@nogc this(int a) { this.a = a; }
>
> 		// the function itself
> 		@nogc int opCall(int b) { return a+b; }
> 	}
>
> 	// capture a by value
>         // WARNING: I stack allocated here but
>         // set it to a global var, this is wrong;
>         // it should probably be malloc'd, but since
>         // I know I am just using it here, it is OK
> 	auto myfunc = MyFunctor(a);
>
> 	dg = &myfunc.opCall;
>
> 	return dg(10);
> }
>
> void main() {
> 	writeln(helper());
> }

typeof(&myfunc.opCall) == int delegate(int b) @nogc

what magic is this? I had no idea that taking the address of 
opCall would give me a delegate.