[RFA] Algorithms vs operator* and operator==

[chris jefferson]

Paolo Carlini wrote:

> Paolo Carlini wrote:
>
>> Can you spot anything wrong with this kind of change? If we agree that
>> it's good, there are quite a few places to tweak, both in stl_algo and
>> in stl_algobase (besides locale_facets ;)
>
>
> *But*, now I remember std::fill and std::fill_n: in order to avoid 
> expensive
> copies when _ValueType is "big", we should probably use temporary vars
> (like __value) *only* when __is_scalar<_ValueType>::_M_type is true...
>
If we could tell if operator* is returning by value or by reference, 
would this problem go away? If it is returning by reference, then we 
simply take that reference and store it. If it returns by value, then if 
we want to take that value more than once, we may as well copy it into a 
variable, as surely a dereference and an assignment (possibly with 
return value optimisation) would be cheaper than 2 dereferences (which 
both return by value)?

Although at the moment I don't believe it's possible to get the return 
value of a function ¬_¬ , would it be stunningly hard to add as a g++ 
extension (and a useful one at that, people always seem to be asking for 
result_of)?

Chris

> Paolo.