Operator overloading -- lets collect some use cases

[Andrei Alexandrescu]

Don wrote:
> Frits van Bommel wrote:
>> 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:
> 
> Sure, you can do it (behaviour inherited from C++), but is that _EVER_ a 
> good idea? I can't think of any cases where that's anything other than a 
> bug-breeder.
> 
>> You can't just arbitrarily substitute between these two.
> I'm still looking for a use case where that substitution doesn't make 
> sense. No-one has yet come up with such a use case. I postulate that it 
> doesn't exist.

Well I forgot whether BigInt is a class, is it? Anyhow, suppose it *is* 
a class and as such has reference semantics. Then a += b modifies an 
object in-situ, whereas a = a + b creates a whole new object and happens 
to bind a to that new object.

Andrei