Re: [boost] Boost.Algorithm design question

Subject: Re: [boost] Boost.Algorithm design question
From: Marshall Clow (mclow.lists_at_[hidden])
Date: 2011-10-06 14:43:18

On Oct 6, 2011, at 11:05 AM, lcaminiti wrote:

> 
> Dave Abrahams wrote:
>> 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<iterator_traits<Iter>::value_type, Val>
> bool none_of_equal ( Iter first, Iter last, Val const& val ) ; // option 1a

That seems right to me.

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

I think you're missing the requirement is that the value passed in be convertible to "iterator_traits<Iter>::value_type", since that is what will happen at the call site.

Given:
        std::vector<int> v ;
        none_of_equal ( v.begin (), v.end (), 3.2 );

you need to capture the fact that the floating point number 3.2 has to be convertible to 'int'.
[ But maybe that's "external" to the function definition ]

> Essentially, I'd think option 1 requires operator== that satisfies
> has_equal_to<iterator_traits<Iter>::value_type, Val>

Yes.

> while option 2
> requires operator== that satisfies
> has_equal_to<iterator_traits<Iter>::value_type>.

Ok - but that's not sufficient.

-- Marshall

Marshall Clow     Idio Software   <mailto:mclow.lists_at_[hidden]>

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