Operator overloading -- lets collect some use cases

[Don]

Weed wrote:
> Don пишет:
>> Weed wrote:
>>> Frits van Bommel пишет:
>>>> Don wrote:
>>>>> Frits van Bommel wrote:
>>>>>> Don wrote:
>>>>>>> A straightforward first step would be to state in the spec that "the
>>>>>>> compiler is entitled to assume that X+=Y yields the same result as
>>>>>>> X=X+Y"
>>>>>> That doesn't hold for reference types, does it?
>>>>> I thought it does? Got any counter examples?
>>>> For any class type, with += modifying the object and + returning a
>>>> new one:
>>> The += operator too should return the object (usually "this")
>> ALWAYS 'this'. It's another feature of operator overloading which is
>> redundant.
> 
> 
> Not always. Can be more convenient to create the new object and to
> return it.
> 
> For example: if it is necessary to return the object containing the
> sorted data those sorting hurriedly at creation of the returned object
> can give a scoring in performance than if the data is sorted in the
> current object after their change.
But then if you have
  y = x+=b;

surely that would give you x and y being different?
Wouldn't you want x to also point to the new object? (OK, as Stewart 
pointed out, you can't!) Otherwise, you have to perform _both_ sorts!