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- // (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
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