Re: [Boost-users] mpl documentation question

Subject: Re: [Boost-users] mpl documentation question
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2012-04-07 05:06:09

Le 07/04/12 09:13, Robert Ramey a écrit :
> Documentation for mpl::less<T>  has the following section:
>
>
> Expression semantics
> For any Integral Constants c1 and c2:
> typedef less<c1,c2>::type r;
>
> Return type:Integral Constant.
> Semantics:Equivalent to
> typedef bool_<  (c1::value<  c2::value)>  r;
>
> typedef less<c1,c2>  r;                    // a
>
> Return type:Integral Constant.
> Semantics:Equivalent to
> struct r : less<c1,c2>::type {};        //b
>
> if //a is used then the following yields bool_<true>
>
> is_same<  less<c1, c2>, r>
>
> if // b is used then the following yields bool_<false>
>
> is_same<  less<c1, c2>, r>
>
> So in what sense are //a and // b equivalent?
>
Hi,
they are not equivalents. The equivalence relation appears via the 
::type access.

is_same<  less<c1, c2>::type, r::type>

should be true_type in both cases.

This is because integral_constant<typename T, T V> defines a nested 
typedef 'type' as itself.

HTH,
Vicente