Re: [boost] [off-topic] why do we not have std::copy_if?

From: Thorsten Ottosen (thorsten.ottosen_at_[hidden])
Date: 2006-03-14 08:08:24

Caleb Epstein wrote:
> I've recently wondered why std::copy doesn't have an analogous std::copy_if:
> 
> template<class InIt, class OutIt, class Pr>
>      OutIt *copy_if*(InIt first, InIt last, OutIt dest, Pr pred);
> 
> 
> that would copy elements to dest where the predicate returns true.  Not
> unlike "grep" in Perl and "filter" in Python.
> 
> The same goal can be achieved with std::remove_copy_if and the use of a
> sense-reversed predicate, but this leads to confusing code IMHO.
> 
> Why wouldn't this be part of the Standard Library, or am I missing something
> ridiculously obvious?

I guess it should have been part of C++98, but didn't make it due to
perhaps time contraints.

With the advent of ranges, we might make *all* the xxx_if versions of 
algorithms redundant by replacing xxx_if( range, pred ) with

xxx( range | filtered( pred ) );

-Thorsten