316 lines
6.5 KiB
Plaintext
316 lines
6.5 KiB
Plaintext
[/
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(C) Copyright Edward Diener 2011,2012
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE_1_0.txt or copy at
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http://www.boost.org/LICENSE_1_0.txt).
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]
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[section:tti_usingMM An example using the Macro Metafunctions]
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[#sectti_usingMM]
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Using the macro metafunctions can be illustrated by first creating some hypothetical
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user-defined type with corresponding nested types and other inner elements.
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With this type we can illustrate the use of the macro metafunctions. This is
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just meant to serve as a model for what a type T might entail from within
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a class or function template where 'T' is a type passed to the template.
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// An enclosing type
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struct AType
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{
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// Type
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typedef int AnIntType; // as a typedef
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struct BType // as a nested type
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{
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struct CType
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{
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};
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};
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// Template
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template <class> struct AMemberTemplate { };
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template <class,class,class> struct AnotherMemberTemplate { };
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template <class,class,int,class,template <class> class,class,long> struct ManyParameters { };
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template <class,class,int,short,class,template <class,int> class,class> struct MoreParameters { };
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// Data
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BType IntBT;
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// Function
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int IntFunction(short) { return 0; }
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// Static Data
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static short DSMember;
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// Static Function
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static int SIntFunction(long,double) { return 2; }
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};
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I will be using the type above just to illustrate the sort of
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metaprogramming questions we can ask of some type T which is passed
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to the template programmer in a class template. Here is what the
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class template might look like:
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#include <boost/tti/tti.hpp>
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template<class T>
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struct OurTemplateClass
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{
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// compile-time template code regarding T
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};
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Now let us create and invoke the macro metafunctions for each of our inner element types,
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to see if type T above corresponds to our hypothetical type above. Imagine this being
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within 'OurTemplateClass' above. In the examples below the same macro is invoked just once
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to avoid ODR violations.
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[heading Type]
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Does T have a nested type called 'AnIntType' ?
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BOOST_TTI_HAS_TYPE(AnIntType)
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has_type_AnIntType
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<
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T
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>
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Does T have a nested type called 'BType' ?
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BOOST_TTI_HAS_TYPE(BType)
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has_type_BType
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<
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T
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>
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[heading Type checking the typedef using a lambda expression]
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Does T have a nested typedef called 'AnIntType' whose type is an 'int' ?
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#include <boost/mpl/placeholders.hpp
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#include <boost/type_traits/is_same.hpp
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using namespace boost::mpl::placeholders;
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has_type_AnIntType
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<
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T,
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boost::is_same<_1,int>
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>
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[heading Template]
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Does T have a nested class template called 'AMemberTemplate' whose template
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parameters are all types ('class' or 'typename') ?
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BOOST_TTI_HAS_TEMPLATE(AMemberTemplate,BOOST_PP_NIL)
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has_template_AMemberTemplate
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<
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T
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>
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[heading Template using variadic macros]
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Does T have a nested class template called 'AMemberTemplate' whose template
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parameters are all types ('class' or 'typename') ?
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BOOST_TTI_HAS_TEMPLATE(AnotherMemberTemplate)
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has_template_AnotherMemberTemplate
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<
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T
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>
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[heading Template with params]
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Does T have a nested class template called 'MoreParameters' whose template
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parameters are specified exactly ?
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BOOST_TTI_HAS_TEMPLATE(MoreParameters,(8,(class,class,int,short,class,template <class,int> class,class)))
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has_template_MoreParameters
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<
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T
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>
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[heading Template with params using variadic macros]
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Does T have a nested class template called 'ManyParameters' whose template
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parameters are specified exactly ?
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BOOST_TTI_HAS_TEMPLATE(ManyParameters,class,class,int,class,template <class> class,class,long)
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has_template_ManyParameters
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<
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T
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>
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[heading Member data]
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Does T have a member data called 'IntBT' whose type is 'AType::BType' ?
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BOOST_TTI_HAS_MEMBER_DATA(IntBT)
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has_member_data_IntBT
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<
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T,
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AType::BType
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>
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[heading Member data with composite type]
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Does T have a member data called 'IntBT' whose type is 'AType::BType' ?
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BOOST_TTI_HAS_MEMBER_DATA(IntBT)
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has_member_data_IntBT
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<
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AType::BType T::*
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>
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[heading Member function with individual types]
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Does T have a member function called 'IntFunction' whose type is
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'int (short)' ?
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BOOST_TTI_HAS_MEMBER_FUNCTION(IntFunction)
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has_member_function_IntFunction
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<
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T,
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int,
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boost::mpl::vector<short>
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>
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[heading Member function with composite type]
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Does T have a member function called 'IntFunction' whose type is
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'int (short)' ?
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BOOST_TTI_HAS_MEMBER_FUNCTION(IntFunction)
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has_member_function_IntFunction
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<
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int (T::*)(short)
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>
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[heading Static member data]
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Does T have a static member data called 'DSMember' whose type is 'short' ?
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BOOST_TTI_HAS_STATIC_MEMBER_DATA(DSMember)
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has_static_member_data_DSMember
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<
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T,
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short
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>
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[heading Static member function with individual types]
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Does T have a static member function called 'SIntFunction' whose type
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is 'int (long,double)' ?
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BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION(SIntFunction)
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has_static_member_function_SIntFunction
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<
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T,
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int,
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boost::mpl::vector<long,double>
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>
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[heading Static member function with composite type]
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Does T have a static member function called 'SIntFunction' whose type
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is 'int (long,double)' ?
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BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION(SIntFunction)
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has_static_member_function_SIntFunction
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<
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T,
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int (long,double)
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>
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[heading Data]
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Does T have a member data or static member data called 'DSMember' whose type is 'short' ?
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BOOST_TTI_HAS_DATA(DSMember)
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has_static_member_data_DSMember
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<
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T,
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short
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>
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[heading Function]
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Does T have a member function or a static member function called 'IntFunction' whose type is
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'int (short)' ?
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BOOST_TTI_HAS_FUNCTION(IntFunction)
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has_function_IntFunction
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<
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T,
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int,
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boost::mpl::vector<short>
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>
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[heading Member type]
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Create a nested type T::BType::CType without creating a compiler error
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if T does not have the nested type BType::CType ?
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BOOST_TTI_MEMBER_TYPE(BType)
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BOOST_TTI_MEMBER_TYPE(CType)
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typename
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member_type_CType
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<
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typename
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member_type_BType
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<
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T
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>::type
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>::type
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[heading Member type existence]
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Does a nested type T::BType::CType, created without creating a compiler error
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if T does not have the nested type BType::CType, actually exist ?
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BOOST_TTI_MEMBER_TYPE(BType)
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BOOST_TTI_MEMBER_TYPE(CType)
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typedef typename
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member_type_CType
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<
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typename
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member_type_BType
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<
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T
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>::type
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>::type
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AType;
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boost::tti::valid_member_type
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<
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AType
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>
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[endsect]
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