Re: How to call destructor before free without dropping @nogc?

[Bienlein via Digitalmars-d-learn]

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.