Re: Copy instead of reference?
On 05/23/13 14:30, Namespace wrote: > On Thursday, 23 May 2013 at 12:29:04 UTC, Artur Skawina wrote: >> On 05/23/13 13:57, Namespace wrote: >>> I know that D has (sadly) no C++ references, but I still think that >>> >>> A a = some_existing_A; >>> >>> should call opAssign. >> >> Not opAssign, but user-defined copy-constructor. But D does not have >> them either... > > That would be a solution. They are required anyway, for several reasons. Right now, you /can/ do: A a = A(some_existing_A); but, because 'A a = some_existing_A' will bypass your cpctor and call the postblit, it's too dangerous. Unless you mark the latter as @disabled, which of course causes other problems. artur
Re: Copy instead of reference?
On Thursday, 23 May 2013 at 12:29:04 UTC, Artur Skawina wrote: On 05/23/13 13:57, Namespace wrote: I know that D has (sadly) no C++ references, but I still think that A a = some_existing_A; should call opAssign. Not opAssign, but user-defined copy-constructor. But D does not have them either... artur That would be a solution.
Re: Copy instead of reference?
On 05/23/13 13:57, Namespace wrote: > I know that D has (sadly) no C++ references, but I still think that > > A a = some_existing_A; > > should call opAssign. Not opAssign, but user-defined copy-constructor. But D does not have them either... artur
Re: Copy instead of reference?
On Thursday, 23 May 2013 at 12:07:40 UTC, Maxim Fomin wrote: On Thursday, 23 May 2013 at 11:57:04 UTC, Namespace wrote: I know that D has (sadly) no C++ references, but I still think that A a = some_existing_A; should call opAssign. Now I see what has you confused. Whether postblit or opAssign is called, depend on left, not right side of assignment. Object 'a' didn't exists prior, so postblit is called, and copy ctor is called with respect of 'a' as 'this' argument. What had confused me, was the point, that it doesn't matter if you return by value or by ref, you get the same output for this specific case. That did not feel right. But thanks to you.
Re: Copy instead of reference?
On Thursday, 23 May 2013 at 11:57:04 UTC, Namespace wrote: I know that D has (sadly) no C++ references, but I still think that A a = some_existing_A; should call opAssign. Actually, it is similar to C++ : http://codepad.org/lkPMU1Ne
Re: Copy instead of reference?
On Thursday, 23 May 2013 at 11:57:04 UTC, Namespace wrote: I know that D has (sadly) no C++ references, but I still think that A a = some_existing_A; should call opAssign. Now I see what has you confused. Whether postblit or opAssign is called, depend on left, not right side of assignment. Object 'a' didn't exists prior, so postblit is called, and copy ctor is called with respect of 'a' as 'this' argument.
Re: Copy instead of reference?
And if I do this: A a; a = b.getA(); I get what I want. What a spasm...
Re: Copy instead of reference?
I know that D has (sadly) no C++ references, but I still think that A a = some_existing_A; should call opAssign.
Re: Copy instead of reference?
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
Re: Copy instead of reference?
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
Re: Copy instead of reference?
On Thursday, 23 May 2013 at 11:31:19 UTC, Simen Kjaeraas wrote:
On Thu, 23 May 2013 13:29:49 +0200, Namespace
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.
Re: Copy instead of reference?
On Thu, 23 May 2013 13:29:49 +0200, Namespace wrote: That was what I also expected. But opAssign is not called. Because you have a postblit. It's called instead of opAssign. -- Simen
Re: Copy instead of reference?
That was what I also expected. But opAssign is not called.
Re: Copy instead of reference?
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
Re: Copy instead of reference?
I've filled a bug report.
Re: Copy instead of reference?
Forget to say: I use dmd 2.062.
Copy instead of reference?
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]
