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      The strength of BOOST_TTI_MEMBER_TYPE
      to represent a type which may or may not exist, and which then can be subsequently
      used in other macro metafunctions whenever a type is needed as a template parameter
      without producing a compiler error, should not be underestimated. It is one
      of the reasons why we have two different ways of using our generated metafunction
      when introspecting for member data, a member function, or a static member function
      of an enclosing type.
    
      In the cases where we specify a composite syntax when using BOOST_TTI_HAS_MEMBER_DATA,
      BOOST_TTI_HAS_MEMBER_FUNCTION,
      or BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION,
      the signature for the member data, member function, or static member function
      is a single type. For BOOST_TTI_HAS_MEMBER_DATA
      the signature is a pointer to member data, for BOOST_TTI_HAS_MEMBER_FUNCTION
      the signature is a pointer to a member function, and for BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION
      the signature is divided between an enclosing type and a function in composite
      format. This makes for a syntactical notation which is natural to specify,
      but because of the notation we can not use the nested type functionality in
      BOOST_TTI_MEMBER_TYPE for potential
      parts of these composite types. If any part of this signature, which specifies
      a composite of various types, is invalid, a compiler time error will occur.
    
      But in the more specific cases, when we use BOOST_TTI_HAS_MEMBER_DATA,
      BOOST_TTI_HAS_MEMBER_FUNCTION,
      and BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION,
      our composite type in our signatures is broken down into their individual types
      so that using BOOST_TTI_MEMBER_TYPE
      for any one of the individual types will not lead to a compile time error if
      the type specified does not actually exist.
    
A few examples will suffice.
      Given known types T and U, and the supposed type Ntype as a nested type of
      U, we want to find out if type T has a member function whose signature is
      void aMemberFunction(U::Ntype).
    
      First using BOOST_TTI_HAS_MEMBER_FUNCTION
      using our composite form we would code:
    
#include <boost/tti/has_member_function.hpp> BOOST_TTI_HAS_MEMBER_FUNCTION(aMemberFunction) has_member_function_aMemberFunction<void (T::*)(U::Ntype)>::value;
If the nested type U::Ntype does not exist, this leads to a compiler error. We really want to avoid this situation, so let's try our alternative.
      Second using BOOST_TTI_HAS_MEMBER_FUNCTION
      using our specific form we would code:
    
#include <boost/tti/member_type.hpp> #include <boost/tti/has_member_function.hpp> BOOST_TTI_HAS_MEMBER_TYPE(Ntype) BOOST_TTI_HAS_MEMBER_FUNCTION(aMemberFunction) typedef typename has_member_type_Ntype<U>::type OurType; has_member_function_aMemberFunction<T,void,boost::mpl::vector<OurType> >::value;
      If the nested type U::Ntype does exist and T does have a member function whose
      signature is void aMemberFunction(U::Ntype) our
      'value' is true, otherwise it is false. We will never get a compiler error
      in this case.
    
      As a second example we will once again use the suppositions of our first example;
      given known types T and U, and the supposed type Ntype as a nested type of
      U. But this time let us look for a static member function whose signature is
      void aStaticMemberFunction(U::Ntype).
    
      First using BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION
      using our composite form we would code:
    
#include <boost/tti/has_static_member_function.hpp> BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION(aStaticMemberFunction) has_static_member_function_aStaticMemberFunction<T,void (U::Ntype)>::value;
Once again if the nested type U::Ntype does not exist, this leads to a compiler error, so let's try our alternative.
      Second using BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION
      using our specific form we would code:
    
#include <boost/tti/member_type.hpp> #include <boost/tti/has_static_member_function.hpp> BOOST_TTI_HAS_MEMBER_TYPE(Ntype) BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION(aStaticMemberFunction) typedef typename has_member_type_Ntype<U>::type OurType; has_static_member_function_aStaticMemberFunction<T,void,boost::mpl::vector<OurType> >::value;
      If the nested type U::Ntype does exist and T does have a member function whose
      signature is void aMemberFunction(U::Ntype) our
      'value' is true, otherwise it is false. We will never get a compiler error
      in this case.