Steven Watanabe wrote:
template <typename geometry_type_1, typename geometry_type_2> typename boost::enable_if< boost::mpl::and_<is_any_polygon_set_type<geometry_type_1>, is_any_polygon_set_type<geometry_type_2>, is_either_polygon_set_type<geometry_type_1, geometry_type_2> >, polygon_set_view<geometry_type_1, geometry_type_2, 3>
::type operator-(const geometry_type_1& lvalue, const geometry_type_2& rvalue) { return polygon_set_view<geometry_type_1, geometry_type_2, 3> (lvalue, rvalue); }
This won't work. In order to instantiate enable_if the compiler must instantiate both of its arguments. That means the compiler will try to instantiate polygon_set_view<> for every time the generic operator - in the stl is used for iterator arithmetic. Any error encountered trying to instantiate polygon_set_view will cause a syntax error and failed compilation even though the and_ evaluates to false. To get around this I have added substitution failure when the first parameter is parsed: template <typename geometry_type_1, typename geometry_type_2> typename requires_1< typename gtl_if<typename gtl_and< typename is_polygon_90_set_type<geometry_type_1>::type, typename is_polygon_90_set_type<geometry_type_2>::type>::type>::type, polygon_90_set_view<geometry_type_1, geometry_type_2, boolean_op::BinaryNot> >::type operator-(const geometry_type_1& lvalue, const geometry_type_2& rvalue) { return polygon_90_set_view<geometry_type_1, geometry_type_2, boolean_op::BinaryNot> (lvalue, rvalue, polygon_90_set_traits<geometry_type_1>::orient(lvalue), boolean_op::BinaryNot()); } requires_1 is equivalent to enable_if, gtl_if returns causes substitution failure unless it receives gtl_yes. I'm hoping MSVC will accept this syntax; gcc does just fine. Regards, Luke