I get this output:

====

----
CTor 42
DTor 0
Return A
Postblit 42
----
DTor 84
DTor 42

====

with the following code. I'm a bit confused about the Postblit. I return by ref so I thought that I get a const ref of the original A.

[code]
import std.stdio;

struct A {
public:
	int id;

	this(int id) {
		writeln("CTor ", id);

		this.id = id;
	}

	this(this) {
		writeln("Postblit ", this.id);

		this.id *= 2;
	}

	~this() {
		writeln("DTor ", this.id);
	}
}

class B {
private:
	A _a = void;

public:
	this() {
		this._a = A(42);
	}

	ref const(A) getA() const {
		writeln("Return A");
		return this._a;
	}
}

void main() {
	writeln("----");
	B b = new B();
	A a = b.getA();
	writeln("----");
}
[/code]

Forget to say: I use dmd 2.062.

I've filled a bug report.

On 05/23/13 11:47, Namespace wrote:
> I get this output:
> 
> ====
> 
> ----
> CTor 42
> DTor 0
> Return A
> Postblit 42
> ----
> DTor 84
> DTor 42
> 
> ====
> 
> with the following code. I'm a bit confused about the Postblit. I return by ref so I thought that I get a const ref of the original A.

>     ref const(A) getA() const {
>         writeln("Return A");
>         return this._a;
>     }

>     A a = b.getA();

You do, but you then assign to another 'A'...

artur

That was what I also expected. But opAssign is not called.

On Thu, 23 May 2013 13:29:49 +0200, Namespace <rswhite4@googlemail.com> wrote:

> That was what I also expected. But opAssign is not called.

Because you have a postblit. It's called instead of opAssign.

-- 
Simen

On Thursday, 23 May 2013 at 11:31:19 UTC, Simen Kjaeraas wrote:
> On Thu, 23 May 2013 13:29:49 +0200, Namespace <rswhite4@googlemail.com> wrote:
>
>> That was what I also expected. But opAssign is not called.
>
> Because you have a postblit. It's called instead of opAssign.

[code]
import std.stdio;
import std.c.string : memcpy;

struct A {
public:
	int id;

	this(int id) {
		writeln("CTor ", id);

		this.id = id;
	}

	this(this) {
		writeln("Postblit ", this.id);

		this.id *= 2;
	}

	void opAssign(ref const A a) {
		writeln("opAssign L: ", a.id);
		this.id = a.id;
	}

	void opAssign(const A a) {
		writeln("opAssign R ", a.id);
		memcpy(&this, &a, A.sizeof);
	}

	~this() {
		writeln("DTor ", this.id);
	}
}

class B {
private:
	A _a;

public:
	this() {
		this._a = A(42);
	}

	ref A getA() {
		writeln("Return A");
		return this._a;
	}
}

void main() {
	B b = new B();
	A a = b.getA();
}
[/code]

Output:
----
CTor 42
opAssign R 42
DTor 42
Return A
Postblit 42
DTor 84
DTor 42
----

Postblit, no opAssign call.

To be more detailed:

I'd expected that the code with 'getA' without ref

[code]
	A getA() {
		writeln("Return A");
		return this._a;
	}
[/code]

would print this output:

----
CTor 42
opAssign R 42
DTor 42
Return A
Postblit 42
opAssign R 84
DTor 84
DTor 42
----

And with 'getA' with ref

[code]
	ref A getA() {
		writeln("Return A");
		return this._a;
	}
[/code]

would print this output:

----
CTor 42
opAssign R 42
DTor 42
Return A
opAssign L 42
DTor 42
DTor 42
----

On 05/23/13 13:34, Namespace wrote:
>     A a = b.getA();
> Postblit, no opAssign call.
> 

You're constructing, not assigning. Try reassigning 'a' to see opAssign in action. It's a bit unintuitive and easy to miss - which I did too, hence my misleading first reply - sorry.

The issue is that D has no ref vars, so you can't really keep the returned refs around, other than passing them to another func.

artur

I know that D has (sadly) no C++ references, but I still think that

A a = some_existing_A;

should call opAssign.