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November 21, 2008
Re: how to use opdot
Steven Schveighoffer wrote:
> "Christopher Wright" wrote
>> Steven Schveighoffer wrote:
>>> Not exactly ;)  The wrapped type is not equivalent to inheritance.
>> No, exactly:
>>
>> class Wrapper(T) : T
>> {
>> T opDot() {}
>> }
> 
> class Wrapper(T) : T
> {
> }
> 
> works just as good ;)
> 
> -Steve 

True, but with opDot, you can swap out the real value. I can think of 
cases in which this would be useful -- a sort of "I'll fill in this 
value later" thing.
November 21, 2008
Re: how to use opdot
Christopher Wright escribió:
> Steven Schveighoffer wrote:
>> "Christopher Wright" wrote
>>> Steven Schveighoffer wrote:
>>>> Not exactly ;)  The wrapped type is not equivalent to inheritance.
>>> No, exactly:
>>>
>>> class Wrapper(T) : T
>>> {
>>> T opDot() {}
>>> }
>>
>> class Wrapper(T) : T
>> {
>> }
>>
>> works just as good ;)
>>
>> -Steve 
> 
> True, but with opDot, you can swap out the real value. I can think of 
> cases in which this would be useful -- a sort of "I'll fill in this 
> value later" thing.

I'm not sure that's the decorator pattern any more. In that pattern you 
implement or extend a class, and receive an instance of one in the 
constructor and forward all calls to that instance. If you do:

class Wrapper(T) : T {

  private wrapped;

  this(T wrapped) {
    this.wrapped = wrapped;
  }

  T opDot() { return wrapped; }

}

that won't work because whenever you call a method of T on Wrapper(T), 
that will call Wrapper's method, since it has it, because it 
extends/implements T (opDot won't be triggered). If you remove 
inheritance, that will probably work, but you won't be able to make a 
Wrapper(T) behave like a T for the type system.
November 21, 2008
Re: how to use opdot
"Ary Borenszweig" wrote
> Christopher Wright escribió:
>> Steven Schveighoffer wrote:
>>> "Christopher Wright" wrote
>>>> Steven Schveighoffer wrote:
>>>>> Not exactly ;)  The wrapped type is not equivalent to inheritance.
>>>> No, exactly:
>>>>
>>>> class Wrapper(T) : T
>>>> {
>>>> T opDot() {}
>>>> }
>>>
>>> class Wrapper(T) : T
>>> {
>>> }
>>>
>>> works just as good ;)
>>>
>>> -Steve
>>
>> True, but with opDot, you can swap out the real value. I can think of 
>> cases in which this would be useful -- a sort of "I'll fill in this value 
>> later" thing.
>
> I'm not sure that's the decorator pattern any more. In that pattern you 
> implement or extend a class, and receive an instance of one in the 
> constructor and forward all calls to that instance. If you do:
>
> class Wrapper(T) : T {
>
>   private wrapped;
>
>   this(T wrapped) {
>     this.wrapped = wrapped;
>   }
>
>   T opDot() { return wrapped; }
>
> }
>
> that won't work because whenever you call a method of T on Wrapper(T), 
> that will call Wrapper's method, since it has it, because it 
> extends/implements T (opDot won't be triggered). If you remove 
> inheritance, that will probably work, but you won't be able to make a 
> Wrapper(T) behave like a T for the type system.

Exactly what I was going to say ;)  If you inherit from a T, then return T 
in an opDot, opDot will never be called unless you call opDot directly.

-Steve
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