Destructors can't be @nogc?

[Tejas]

On Friday, 23 July 2021 at 20:24:02 UTC, Jim wrote:
> Hello,
>
> I've been playing with D and trying to understand how to work 
> with @nogc. I must be doing something wrong, because even 
> though I tagged the destructor for my class `@nogc`, I'm 
> getting the following error: `.\min.d(27): Error: "@nogc" 
> function "D main" cannot call non- at nogc function 
> "object.destroy!(true, TestClass).destroy`
>
> ```D
> import std.stdio : printf;
> import core.lifetime : emplace;
> import core.stdc.stdlib : malloc, free;
>
> class TestClass {
>     int x;
>
>     this(int x) @nogc {
>         printf("TestClass's constructor called\n");
>         this.x = x;
>     }
>
>
>     ~this() @nogc {
>         printf("TestClass's destructor called\n");
>     }
> }
>
> @nogc void
> main() {
>     auto size = __traits(classInstanceSize, TestClass);
>     auto memory = malloc(size)[0..size];
>     TestClass x = emplace!(TestClass)(memory, 1);
>
>     printf("TestClass.x = %d\n", x.x);
>
>     destroy(x);
>     free(cast(void*)x);
> }
>
> ```
>
> What is the problem here? Should I not call `destroy`? If so, 
> what should I call instead?

Try using the ```scope``` storage class. You will lose the 
ability to explicitly call the destructor, but maybe it is good 
enough for your purposes.

The following works:

```d
import std.stdio : printf;
import core.lifetime : emplace;
import core.stdc.stdlib : malloc, free;

     class TestClass {
         int x;

         this(int x) @nogc {
             printf("TestClass's constructor called\n");
             this.x = x;
         }


         ~this() @nogc {
             printf("TestClass's destructor called\n");
         }
     }

     @nogc void
     main() {
         //auto size = __traits(classInstanceSize, TestClass);
         //auto memory = malloc(size)[0..size];
         scope /*notice the scope storage class*/TestClass x =  
new TestClass(1);// emplace!(TestClass)(memory, 1);

         printf("TestClass.x = %d\n", x.x);

         //destroy(x);
         //free(cast(void*)x);
     }
```

If you absolutely want to be able to explicitly call the 
destructor, then custom functions are the only option, 
unfortunately.