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## Macro BOOST_TTI_TRAIT_HAS_DATA

BOOST_TTI_TRAIT_HAS_DATA — A macro which expands to a metafunction which tests whether member data or static member data with a particular name and type exists.

## Synopsis

    // In header: <boost/tti/has_data.hpp>

    BOOST_TTI_TRAIT_HAS_DATA(trait, name)

## Description

BOOST_TTI_TRAIT_HAS_DATA is a macro which expands to a metafunction. The metafunction tests whether member data or static member data with a particular name and type exists. The macro takes the form of BOOST_TTI_TRAIT_HAS_DATA(trait,name) where

trait = the name of the metafunction
name = the name of the inner data.

BOOST_TTI_TRAIT_HAS_DATA generates a metafunction called "trait" where 'trait' is the macro parameter.

    template<class BOOST_TTI_TP_T,class BOOST_TTI_TP_TYPE>
    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'
                          The enclosing type can be a class, struct, or union.
                          If the type is a union, static member data can only
                          be found if the C++11 unrestricted union is implemented
                          by the compiler being used, since prior to C++11 a union
                          could not have static data members.

      BOOST_TTI_TP_TYPE = The type of the member data or static member.

      returns  = 'value' is true if the 'name' exists, with the correct data type,
                 otherwise 'value' is false.