Brent Spillner wrote:
On Thu, 22 Sep 2011 10:30:14 lcaminiti wrote:
I think this can be achieved with my previous "option 2" suggestion:
namespace dummy { template< typename L, typename R> bool operator== ( L const&, R const& ) { return true; } }
postcondition( using dummy::operator==, back() == value )
This will fail if L has a private (or protected) operator==.
Let me understand your point a bit better. I think you mean something like this: #include <boost/type_traits/can_call_equal.hpp> #include <vector> #include <iostream> #include <cassert> namespace dummy { template< typename L, typename R > bool operator== ( L const& left, R const& right ) { std::clog << "dummy ==\n"; return true; } } template< typename T > struct vect { void push_back ( T const& value ) { v_.push_back(value); using dummy::operator==; assert( back() == value ); } T const& back ( ) const { return v_.back(); } private: std::vector<T> v_; }; struct val { private: bool operator== ( val const& right ) const { std::clog << "val ==\n"; return true; } }; int main ( ) { vect<val> v; v.push_back(val()); // error 1 std::cout << boost::can_call_equal<val>::value << std::endl; // error 2 return 0; }; In this case T = val has an operator== which is private. This causes both the methods (1) using dummy::operator== and (2) the traits requirement can_call_equal<val> to fail :( Ideally, can_call_equal<val>::value will return false instead of generating a compiler-error when val::operator== is private or protected. A part from such an (impossible?) improvement to can_call_equal, I have no solution for this issue. I can document it and at the end the library users are responsible to program contracts with assertion requirements that can be checked within C++ (and can_call_equal<val> when val has a private operator== cannot be checked so it's simply a ill-formed assertion requirement). What do you think? --Lorenzo -- View this message in context: http://boost.2283326.n4.nabble.com/boost-contract-extra-type-requirements-fo... Sent from the Boost - Dev mailing list archive at Nabble.com.