Re: [Boost-users] mpl documentation question

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::type r;

Return type:Integral Constant. Semantics:Equivalent to typedef bool_< (c1::value< c2::value)> r;

typedef less r; // a

Return type:Integral Constant. Semantics:Equivalent to struct r : less::type {}; //b

if //a is used then the following yields bool_<true>

is_same< less, r>

if // b is used then the following yields bool_<false>

is_same< less, 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::type, r::type> should be true_type in both cases. This is because integral_constant defines a nested typedef 'type' as itself. HTH, Vicente