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## Macro BOOST_TTI_TRAIT_MEMBER_TYPE

BOOST_TTI_TRAIT_MEMBER_TYPE — Expands to a metafunction whose typedef 'type' is either the named type or a marker type.

## Synopsis

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

    BOOST_TTI_TRAIT_MEMBER_TYPE(trait, name)

## Description

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_MARKER_TYPE = boost::tti::detail::notype> struct trait { typedef unspecified type; typedef BOOST_TTI_TP_MARKER_TYPE boost_tti_marker_type; }; The metafunction types and return: BOOST_TTI_TP_T = the enclosing type. BOOST_TTI_TP_MARKER_TYPE = (optional) a type to use as the marker type. defaults to the internal boost::tti::detail::notype. returns = 'type' is the inner type of 'name' if the inner type exists within the enclosing type, else 'type' is a marker type. if the end-user does not specify a marker type then an internal boost::tti::detail::notype marker type is used. The metafunction also encapsulates the type of the marker type as a nested 'boost_tti_marker_type'.

The purpose of this macro is to encapsulate the 'name' type as the typedef 'type' of a metafunction, but only if it exists within the enclosing type. This allows for an evaluation of inner type existence, without generating a compiler error, which can be used by other metafunctions in this library.