Scope variables.

[Agustin]

On Monday, 7 October 2013 at 22:57:17 UTC, Ali Çehreli wrote:
> On 10/07/2013 03:52 PM, Agustin wrote:
>> On Monday, 7 October 2013 at 19:59:09 UTC, Agustin wrote:
>>> On Monday, 7 October 2013 at 19:58:21 UTC, Agustin wrote:
>>>> I'm having a hard time trying to use "scoped".
>>>>
>>>> public T callEvent(T, A...)(auto ref A args) const
>>>> {
>>>> T pEvent = scoped!T(forward!args);
>>>> postEvent(pEvent, typeid(T).toHash);
>>>> return pEvent;
>>>> }
>>>>
>>>> private void postEvent(ref Event event, Event.ID type) const
>>>> {
>>>> ....
>>>> }
>>>>
>>>> src\event\EventManager.d(37): Error: function
>>>> ghrum.event.EventManager.EventManager.postEvent (ref Event 
>>>> event,
>>>> uint type) const is not callable using argument types 
>>>> (MyEvent,uint)
>>>> src\event\EventManager.d(37): Error: function
>>>> ghrum.event.EventManager.EventManager.postEvent (ref Event 
>>>> event,
>>>> uint type) const is not callable using argument types 
>>>> (MyEvent,uint)
>>>> const
>>>> src\event\EventManager.d(37): Error: cast(Event)pEvent is 
>>>> not an lvalue
>>>
>>>
>>> callEvent!MyEvent(); Being MyEvent a subclass of Event.
>>
>> So i found out that i cannot do this, may i ask why?
>>
>> public class A
>> {
>>   int x = 0;
>> }
>>
>> public class B : A
>> {
>> }
>>
>> void func(ref A a)
>> {
>> }
>>
>> void main()
>> {
>>   B b = new B();
>>   func(b);
>> }
>
> Since classes are already references, you would normally pass 
> A, not 'ref A'.
>
> If you really want to pass 'ref A', perhaps you want to change 
> the actual object that an A is referring to:
>
> public class C : A
> {}
>
> void func(ref A a)
> {
>     a = new C;    // <-- A reason for taking 'ref A'
> }
>
> However, that would upset the caller, which thinks it has a 
> reference to a B object:
>
> void main()
> {
>   B b = new B();
>   func(b);        // <-- Oops! Not a B anymore?
> }
>
> Ali

Doesn't ref means i'm passing the parameter by reference instead 
of by value?. Isn't "a" being copied when calling func?, or does 
D always pass by reference when using classes and structures?