Re: [boost] Boost.Algorithm design question

Subject: Re: [boost] Boost.Algorithm design question
From: Dave Abrahams (dave_at_[hidden])
Date: 2011-10-29 15:25:13

on Sat Oct 29 2011, "Peter Dimov" <pdimov-AT-pdimov.com> wrote:

> Dave Abrahams wrote:
>
>> Here's another reason why the first formulation might not be such a hot
>> idea: it rules out some obvious implementations that really ought to be
>> OK.  For example,
>>
>>       template <class InputIterator, class T>
>>       InputIterator find(InputIterator i, InputIterator j, T value)
>>       {
>>           while (i != j && !(*i == value))
>>               ++i;
>>           return i;
>>       }
>
> Yes, but this formulation doesn't need *i and value to be of the same
> type or operator== to be an equivalence relation. It just needs
> operator== to return something bool-ish. 

Actually it needs a bit more than that: applying ! to your bool-ish
thing needs to be unambiguously &&-able with the result of i != j, which
might not itself be bool.  These are the kinds of problems that crop up
when you start checking constraints on valid expressions.

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com