Hello,
Why is copy ctor in this example not called?

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.

On Sunday, 19 December 2021 at 22:29:21 UTC, vit wrote:

Because D runtime isn't properly married to copy constructors yet. I.e. it's a bug, a variant of this one: https://issues.dlang.org/show_bug.cgi?id=20879

On Sunday, 19 December 2021 at 22:29:21 UTC, vit wrote:

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();
}

init: 1
init: 2
~dtor:1
~dtor:2
~dtor:1

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

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
+/

On Sunday, 19 December 2021 at 23:21:00 UTC, Stanislav Blinov wrote:

Thanks,
That bug is 1.5 years old. Are this problems with copy ctors hard to fix?
Are copy ctors still experimental functionality?