How to call destructor before free without dropping @nogc?

[Bienlein]

On Thursday, 19 August 2021 at 07:30:38 UTC, Bienlein wrote:
> Hello,
>
> I allocate some instance of class C manually and then free the 
> memory again:
>
>     class C {
>         int num;
>
>         ~this() {
>     	writeln("~this");
>         }
>     }
>
>     void foo() // @nogc
>     {
>         auto mem = cast(C)malloc(__traits(classInstanceSize, 
> C));
>         auto c = emplace!(C)(mem);
>
>         c.num = 789;
>
>         destroy(c);
>         free(cast(void*) c);
>         c = null;
>     }
>
>     int main()
>     {
>     	foo();
>     }
>
> The code above works well as the destructor of c in class C is 
> called by destroy. Problem is that destroy cannot be used once 
> function foo is annotated with @nogc. There seems to be no way 
> round it.
>
> What I want is to keep the function foo annotated with @nogc, 
> but still have the destructor of C be called before free is 
> called. Is there a way to call the destructor through meta 
> programming or some kind of reflection so that I can create 
> some generic function that calls the destructor and then free 
> for any kind of class?
>
> Thanks, Bienlein

Oops, I just realized that you can also not call emplace when 
@nogc is present. Well that is at least consistent with not 
either being able to call destroy ;-).

So, I guess this means that you can forget about manually 
allocating and freeing some instance of a class and using @nogc 
as well. That's a pitty, @nogc was a good idea.