| |
| // (C) Copyright Edward Diener 2011,2012,2013 |
| // Use, modification and distribution are subject to the Boost Software License, |
| // Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at |
| // http://www.boost.org/LICENSE_1_0.txt). |
| |
| #if !defined(BOOST_TTI_HAS_TYPE_HPP) |
| #define BOOST_TTI_HAS_TYPE_HPP |
| |
| #include <boost/config.hpp> |
| #include <boost/preprocessor/cat.hpp> |
| #include <boost/tti/gen/has_type_gen.hpp> |
| #include <boost/tti/gen/namespace_gen.hpp> |
| #include <boost/tti/detail/dtype.hpp> |
| #include <boost/tti/detail/ddeftype.hpp> |
| |
| /* |
| |
| The succeeding comments in this file are in doxygen format. |
| |
| */ |
| |
| /** \file |
| */ |
| |
| /** |
| |
| BOOST_TTI_TRAIT_HAS_TYPE is a macro which expands to a metafunction. |
| The metafunction tests whether an inner type with a particular name exists |
| and, optionally, whether a lambda expression invoked with the inner type |
| is true or not. |
| |
| trait = the name of the metafunction within the tti namespace. |
| |
| name = the name of the inner type. |
| |
| generates a metafunction called "trait" where 'trait' is the macro parameter. |
| |
| template<class BOOST_TTI_TP_T,class BOOST_TTI_TP_U> |
| struct trait |
| { |
| static const value = unspecified; |
| typedef mpl::bool_<true-or-false> type; |
| }; |
| |
| The metafunction types and return: |
| |
| BOOST_TTI_TP_T = the enclosing type in which to look for our 'name'. |
| |
| BOOST_TTI_TP_U = (optional) An optional template parameter, defaulting to a marker type. |
| If specified it is an MPL lambda expression which is invoked |
| with the inner type found and must return a constant boolean |
| value. |
| |
| returns = 'value' depends on whether or not the optional BOOST_TTI_TP_U is specified. |
| |
| If BOOST_TTI_TP_U is not specified, then 'value' is true if the 'name' type |
| exists within the enclosing type BOOST_TTI_TP_T; otherwise 'value' is false. |
| |
| If BOOST_TTI_TP_U is specified , then 'value' is true if the 'name' type exists |
| within the enclosing type BOOST_TTI_TP_T and the lambda expression as specified |
| by BOOST_TTI_TP_U, invoked by passing the actual inner type of 'name', returns |
| a 'value' of true; otherwise 'value' is false. |
| |
| The action taken with BOOST_TTI_TP_U occurs only when the 'name' type exists |
| within the enclosing type BOOST_TTI_TP_T. |
| |
| Example usage: |
| |
| BOOST_TTI_TRAIT_HAS_TYPE(LookFor,MyType) generates the metafunction LookFor in the current scope |
| to look for an inner type called MyType. |
| |
| LookFor<EnclosingType>::value is true if MyType is an inner type of EnclosingType, otherwise false. |
| |
| LookFor<EnclosingType,ALambdaExpression>::value is true if MyType is an inner type of EnclosingType |
| and invoking ALambdaExpression with the inner type returns a value of true, otherwise false. |
| |
| A popular use of the optional MPL lambda expression is to check whether the type found is the same |
| as another type, when the type found is a typedef. In that case our example would be: |
| |
| LookFor<EnclosingType,boost::is_same<_,SomeOtherType> >::value is true if MyType is an inner type |
| of EnclosingType and is the same type as SomeOtherType. |
| |
| */ |
| #define BOOST_TTI_TRAIT_HAS_TYPE(trait,name) \ |
| BOOST_TTI_DETAIL_TRAIT_HAS_TYPE(trait,name) \ |
| template \ |
| < \ |
| class BOOST_TTI_TP_T, \ |
| class BOOST_TTI_TP_U = BOOST_TTI_NAMESPACE::detail::deftype \ |
| > \ |
| struct trait \ |
| { \ |
| typedef typename \ |
| BOOST_PP_CAT(trait,_detail_type)<BOOST_TTI_TP_T,BOOST_TTI_TP_U>::type type; \ |
| BOOST_STATIC_CONSTANT(bool,value=type::value); \ |
| }; \ |
| /**/ |
| |
| /** |
| |
| BOOST_TTI_HAS_TYPE is a macro which expands to a metafunction. |
| The metafunction tests whether an inner type with a particular name exists |
| and, optionally, whether a lambda expression invoked with the inner type |
| is true or not. |
| |
| name = the name of the inner type. |
| |
| generates a metafunction called "has_type_'name'" where 'name' is the macro parameter. |
| |
| template<class BOOST_TTI_TP_T,class BOOST_TTI_TP_U> |
| struct has_type_'name' |
| { |
| static const value = unspecified; |
| typedef mpl::bool_<true-or-false> type; |
| }; |
| |
| The metafunction types and return: |
| |
| BOOST_TTI_TP_T = the enclosing type in which to look for our 'name'. |
| |
| BOOST_TTI_TP_U = (optional) An optional template parameter, defaulting to a marker type. |
| If specified it is an MPL lambda expression which is invoked |
| with the inner type found and must return a constant boolean |
| value. |
| |
| returns = 'value' depends on whether or not the optional BOOST_TTI_TP_U is specified. |
| |
| If BOOST_TTI_TP_U is not specified, then 'value' is true if the 'name' type |
| exists within the enclosing type BOOST_TTI_TP_T; otherwise 'value' is false. |
| |
| If BOOST_TTI_TP_U is specified , then 'value' is true if the 'name' type exists |
| within the enclosing type BOOST_TTI_TP_T and the lambda expression as specified |
| by BOOST_TTI_TP_U, invoked by passing the actual inner type of 'name', returns |
| a 'value' of true; otherwise 'value' is false. |
| |
| The action taken with BOOST_TTI_TP_U occurs only when the 'name' type exists |
| within the enclosing type BOOST_TTI_TP_T. |
| |
| Example usage: |
| |
| BOOST_TTI_HAS_TYPE(MyType) generates the metafunction has_type_MyType in the current scope |
| to look for an inner type called MyType. |
| |
| has_type_MyType<EnclosingType>::value is true if MyType is an inner type of EnclosingType, otherwise false. |
| |
| has_type_MyType<EnclosingType,ALambdaExpression>::value is true if MyType is an inner type of EnclosingType |
| and invoking ALambdaExpression with the inner type returns a value of true, otherwise false. |
| |
| A popular use of the optional MPL lambda expression is to check whether the type found is the same |
| as another type, when the type found is a typedef. In that case our example would be: |
| |
| has_type_MyType<EnclosingType,boost::is_same<_,SomeOtherType> >::value is true if MyType is an inner type |
| of EnclosingType and is the same type as SomeOtherType. |
| |
| */ |
| #define BOOST_TTI_HAS_TYPE(name) \ |
| BOOST_TTI_TRAIT_HAS_TYPE \ |
| ( \ |
| BOOST_TTI_HAS_TYPE_GEN(name), \ |
| name \ |
| ) \ |
| /**/ |
| |
| #endif // BOOST_TTI_HAS_TYPE_HPP |