[boost] Re: Formal Review: FOREACH macro

From: David Abrahams (dave_at_[hidden])
Date: 2005-05-02 19:40:17

"Gennadiy Rozental" <gennadiy.rozental_at_[hidden]> writes:

>>> And dangerous. Cause allows developer to "forget" about an extra
>>> copy.
>>
>> I'm not sure where you think the "extra" copy is.  The copy is already
>> implicit in the RHS expression, isn't it?
>
> No. In this case we could control the copy.
>
> collection foo();
>
> returns temporary. FOREACH make copy of this temporary into another 
> temporary. 

Are you sure that copy can't be elided?

> This is an extra copy. Which we could easily control/eliminate 
> with
>
> collection const& c = foo();
>
> statement.
>
>> In general C++ will make lots of copies you can't control.  Extra
>> copies are hardly "dangerous" (except maybe with auto_ptr).  They may
>> be inefficient, but then I don't believe in trying to prevent people
>> from writing inefficient code, especially when that's more convenient.
>> Very little of the code end users write actually needs to be fast.
>
> That's true.  But danger in this case caused by the fact that FOREACH make 
> an extra copy silently. 

Not danger; inefficiency.

> Ok. I agree to keep this functionality. But there 
> should be a bug disclaimer about this overhead.

Not bug... I don't know what.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com