dynamic array + copy ctor

[Tejas]

On Sunday, 19 December 2021 at 22:29:21 UTC, vit wrote:
> Hello,
> Why is copy ctor in this example not called?
>
> ```d
> import std.stdio;
>
> struct Foo {
>     int i;
>
>     this(int i){
>         this.i = i;
>         writeln("init: ", i);
>     }
>
>     this(ref typeof(this) rhs){
>         this.i = rhs.i;
>         writeln("copy: ", i);
>     }
>     ~this() {
>         writeln("~dtor:", i);
>     }
> }
>
> void main(){
>     Foo[] foos;
>
>     foos ~= Foo(1);
>
>     while(foos.capacity > foos.length)
>         foos ~= Foo(0);
>
>     foos ~= Foo(2);
>
>     import core.memory;
>     GC.collect();
> }
> ```
> result:
> ```
> init: 1
> init: 2
> ~dtor:1
> ~dtor:2
> ~dtor:1
> ```
>
> First Foo is destructed 2x.

Yeah, Stanislov is right, it's using a blit rather  than a copy 
constructor:

```d
import std.stdio;

struct Foo {
     int i;

     this(this){
     	writeln("blit: ", i);
     }
     this(int i){
         this.i = i;
         writeln("init: ", i);
     }

     this(scope ref Foo rhs){
         this.i = rhs.i;
         writeln("copy: ", i);
     }
     ~this() {
         writeln("~dtor:", i);
         writeln("~dtor:", &this);
     }
}

void main()  {
     Foo[] foos ;

     foos ~= Foo(1);
     foos ~= Foo(2);
}

/+ Output:
init: 1
init: 2
blit: 1
~dtor:1
~dtor:7EFE0DCD3000
~dtor:2
~dtor:7EFE0DCD4004
~dtor:1
~dtor:7EFE0DCD4000
+/
```