Returning a struct by reference

[Simon TRENY]

grauzone Wrote:

> Simon TRENY wrote:
> > grauzone Wrote:
> > 
> >> Simon TRENY wrote:
> >>> Hi there!
> >>>
> >>> I'm quite new at D and I'm still just playing with it, but there is a thing that I find currently missing. Sometimes, I'd like to be able to return a struct by reference and not by value. For example, in the following example:
> >>>
> >>> struct Position {
> >>>    float x;
> >>>    float y;
> >>> }
> >>>
> >>> class Object {
> >>>    private Position m_position;
> >>>
> >>>    public Position position() {
> >>>       return m_position;
> >>>    }
> >>> }
> >>>
> >>> I'd like to be able to write things like this: myObject.position.x = 43 to actually change the position of the object. But right now, since "position" is a struct, it is returned by value and not by reference, and then the previous instruction won't change the position of the object, but it will work on a copy of the position field.
> >>>
> >>>
> >>> Here is the solutions that I can see to this problem:
> >>>
> >>> - Returning a pointer to the position: "public Position *position() { ... }", but I'd like to keep my code as free from pointers as possible.
> >>>  - Make "Position" a class and not a struct. That could be a solution, but then, when I'll do things like "Position pos = object.position; pos.x = 43;", it will effectively change the position of the object, which I wouldn't like with this syntax.
> >>>
> >>> Actually, I'd like to be able to do a thing like this:
> >>>    public ref Position position() {
> >>>       return m_position;
> >>>    }
> >>> which would be the equivalent form to passing structs by reference in a parameter.
> >>>
> >>> Is there a way to do this in D?
> >> Yes. Make the variable public.
> >>
> >> class Object {
> >> 	Position position;
> >> }
> >>
> >> This code is even simpler than your's above. Incredible, isn't it?
> > 
> > Ok, but then, what if I'd like to make the variable "read-only"? i.e. preventing the user from writing things like this:
> > myObject.position = pos2;
> 
> Then you write a getter that simply returns the field by value.
> 
> The D compiler will (hopefully) inline the getter function, so there 
> shouldn't be a disadvantage in performance.

If I add a getter-property that returns the field by value, the following instruction "object.position.x = 12;" won't modify the position of the object, but will only modify the returned copy of the position, right?
That's actually why I'd like to have a getter that returns the field by reference and not by value.

> 
> Note: I think D2.0 wants to introduce ref-returns at some point in the 
> future.
> 
> >>> Regards,
> >>> Simon
> >>>
> >