Operator overloading -- lets collect some use cases

[Frits van Bommel]

Don wrote:
> Andrei Alexandrescu wrote:
>> 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.
> 
> You're right, though BigInt is not a class. I have, though, seen a 
> BigIntRef class (in Diemos, I think) which behaved in that way. AFAIK, 
> the reason it existed was that the only way you can enforce value 
> semantics in D1 is via copy-on-write, which results in many unnecessary 
> heap allocations and copies.
> So Fritz is correct, it could not be enforced for reference types.

First of all, please note that I'm not German so my name ends with an 
's', not a 'z'.

> The question then is, when are reference semantics desired for an object 
> with arithmetical operator overloading?
> 
> For matrix slices, maybe? But even then I'm not certain you'd want to 
> allow X=X+Y; you'd probably want to use X[]=X[]+Y[].

I never said it'd be useful to use arithmetic ops with classes. In fact, 
my suggestion was to just only apply these transformations to structs 
since they probably wouldn't be very useful for classes anyway.