Re: [boost] Boost.Algorithm design question

Subject: Re: [boost] Boost.Algorithm design question
From: lcaminiti (lorcaminiti_at_[hidden])
Date: 2011-10-06 14:05:07

Dave Abrahams wrote:
> 
> I don't think you can evaluate these choices just by looking at the
> implementations.  Before anyone else votes option 1, I'd like to see
> 

Well, I'm not so sure I like option 1 anymore... if option 1 was an
oversight in STL then there is no sense in perpetuating the specification
error in Boost.Algorithm (perhaps Boost.Algorithm should then go with option
2 and explain the rationale of why it's different than what STL does for
example with std::find).

> somebody write the description of the algorithm, including the concept
> requirements.  With option 2, we know that == has to be an equivalence
> relation.  The semantics in option 1 are a lot fuzzier.
> 

Good point! I'll try to start :)

template< typename Iter, typename Val >
    requires
        InputIterator<Iter>, 
        EqualityComparable&lt;iterator_traits&lt;Iter&gt;::value_type, Val>
bool none_of_equal ( Iter first, Iter last, Val const& val ) ; // option 1a

template< typename Iter >
    requires
        InputIterator<Iter>, 
        EqualityComparable&lt;iterator_traits&lt;Iter&gt;::value_type>
bool none_of_equal ( Iter first, Iter last,
iterator_traits<Iter>::value_type const& value ) ; // option 2

Essentially, I'd think option 1 requires operator== that satisfies
has_equal_to&lt;iterator_traits&lt;Iter&gt;::value_type, Val> while option 2
requires operator== that satisfies
has_equal_to&lt;iterator_traits&lt;Iter&gt;::value_type>.

The alternative would be for option 1 to require instead:

template< typename Iter, typename Val >
    requires
        InputIterator<Iter>, 
        EqualityComparable&lt;iterator_traits&lt;Iter&gt;::value_type>,
        Convertible&lt;Val, iterator_traits&lt;Iter&gt;::value_type>
bool none_of_equal ( Iter first, Iter last, Val const& val ) ; // option 1b

What do you think?

Thanks,
--Lorenzo

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