[boost] Re: [range] rationale for transform_range() algorithm?

From: Eric Niebler (eric_at_[hidden])
Date: 2005-03-14 14:26:37

Thorsten Ottosen wrote:
> "Eric Niebler" <eric_at_[hidden]> wrote in message 

> 
> | But thinking of this
> | as a range conversion is the right way to go, IMO, except that it should
> | be called "range_cast" and it should be explicit.
> 
> hm..I dunno, the cast stuff implies some kind of extra work to me.
> 

Could you explain this a bit?

> | I agree this functionality is useful, but this is a rather unfortunate
> | interface choice, in my opinion. For instance, what if I want to copy to
> | an array:
> |
> | int rg[3] = copy_range<int[3]>(aRange); // oops, can't return array
> 
> if we had
> 
> template< class T, class Range >
> T copy_to_seq( const Range& r )
> {
>     T t;
>     t.assign(begin(r),end(r));
>     return t;
> }
> 
> support of boost::array<T,size> could be ok.

copy(from, to). That's the idiomatic way of writing a copy function. 
What you have above is a conversion function, and typically we call 
those things casts.

> 
> | All these problems are handled nicely by the std::copy algorithm, which
> | takes an output iterator as a parameter. A general, extensible
> | range-based algorithm library should take output /ranges/ as parameters,
> |  or even just an output iterator, but this is all beside the point
> 
> The iterator interface suffers
> from either being slow or being unsafe, so I don't think that is the way to go 
> either.

You're saying that either an output iterator is range-checked and it's 
slow, or it's not an it's unsafe. How is an output range any different? 
It's a sincere question -- I really don't know if output ranges have 
anything to offer above output iterators.

> 
> |. A
> | range-based copy algorithm should have a different interface and be part
> | of a complete range-based algorithms library.
> 
> yes, agreed.
> 
> We just need somebody to write those special range algorithms.
> 

Have you missed it? I've got one in the sandbox, but it needs attention.

-- 
Eric Niebler
Boost Consulting
www.boost-consulting.com