On Thu, Oct 23, 2014 at 10:39:34AM +0530, Shriramana Sharma via Digitalmars-d-learn wrote:
> IIUC the whole deal with not allowing ref parameters to point to rvalues is the fear that they may be returned outside the function, but it seems this is already possible:
> 
> module reftest ;
> import std.stdio ;
> struct Pair {
> 	int x, y ;
> 	this (int x_, int y_) { x = x_ ; y = y_ ; writeln("Pair constructed") ; }
> 	auto handle() { return this ; }
> }
> void main() {
> 	auto P = Pair(1, 2).handle ;
> 	writeln(typeof(P).stringof) ;
> 	P.x = 3 ;
> 	writeln(P.x, ' ', P.y) ;
> }
> 
> Running this makes it clear that only the one Pair object is ever constructed. But I don't understand how it is that the type of P is Pair and not ref(Pair).
[...]

ref is a storage class, not a type constructor. There is actually no
such type as ref(Pair).  The 'ref' applies only to the function
parameter (or return value), NOT to whatever it gets assigned to.


T

-- 
Microsoft is to operating systems & security ... what McDonalds is to gourmet cooking.

Hi thanks for the reply.

So should I understand that "return this" doesn't really return the ref but the object actually? Or it does return a reference but since it's assigned a name, it lives on under that name and so only the single struct object P is ever created? Otherwise one would wonder how a temporary can have lifetime beyond the line in which it is created.

I'd really like to know what's exactly happening in that line:

auto P = Pair(1, 2).handle ;

Thanks!


-- 
Shriramana Sharma ஶ்ரீரமணஶர்மா श्रीरमणशर्मा

On Thu, 23 Oct 2014 16:55:52 +0530
Shriramana Sharma via Digitalmars-d-learn
<digitalmars-d-learn@puremagic.com> wrote:

> I'd really like to know what's exactly happening in that line:
> 
> auto P = Pair(1, 2).handle ;
object moving. add postblit (`this (this)`) and you'll see that.

On Thu, 23 Oct 2014 14:36:17 +0300
ketmar via Digitalmars-d-learn <digitalmars-d-learn@puremagic.com>
wrote:

> On Thu, 23 Oct 2014 16:55:52 +0530
> Shriramana Sharma via Digitalmars-d-learn
> <digitalmars-d-learn@puremagic.com> wrote:
> 
> > I'd really like to know what's exactly happening in that line:
> > 
> > auto P = Pair(1, 2).handle ;
> object moving. add postblit (`this (this)`) and you'll see that.
or, to be precise, object *copying*. it's not the same as creating new object. if you'll add destructor, you'll see that destructor is called twice: once for local copy and once for P.