Re: [boost] [Range] initial feedback on return values of algorithms

From: David Abrahams (dave_at_[hidden])
Date: 2006-02-03 10:08:41

Thorsten Ottosen <tottosen_at_[hidden]> writes:

> David Abrahams wrote:
>> Thorsten Ottosen <tottosen_at_[hidden]> writes:
>> 
>> 
>>>Eric Niebler wrote:
>>>
>
>>>right, but do you also waht sort() to return the sorted range?
>> 
>> 
>> Yes, but as a "reference" to the original, i.e.  a boost::range
>> iterator bundle.
>
> I assume you mean iterator_range< range_iterator<Rng>::type >
> or something similar.

Yes.

>>>>There are lots more issues with range algorithms that have not been 
>>>>discussed yet. What about algorithms that accept an output iterator and 
>>>>write into it? Will they now take an output range? 
>>>
>>>My say would be no. We still have the concept of an unbounded iterator.
>> 
>> There is also the issue of O(1) size, for which you have not got
>> support in your concept hierarchy.  
>
> Did I forget to mention this? Anyway, size() is now O(1). If you want
> a generic version, dictance(rng) is supplied instead.

That's not what I mean.  Is there a way to distinguish, at
compile-time, a range that has support for O(1) size from one that
does not?  One needs that for important "benefit and
beauty"-destroying optimzations that you dislike so.

>  > And then there's property maps.
>
> How do they relate to this?

They're an important part of a generalized range concept.

>>>>And what does br::copy return? You might think the answer is easy: the 
>>>>range designating the unused elements at the end of the second range. 
>>>>But what if br::copy is range-checked and truncates? That return value 
>>>>is no longer sufficient -- if br::copy returns an empty range, did the 
>>>>algorithm truncate, or did it all just fit?
>>>
>>>I'd be quite happy with copy returning void.
>> 
>> 
>> I think that's a mistake.
>
> What do you want it to return then?

A range.  I'm not sure which range.  But I guess I'm not thinking too
carefully about that one, so I retract my previous statement.  I just
don't know.

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