Synopsis

#define BOOST_MPL_HAS_XXX_TRAIT_DEF(name) \
    unspecified token sequence \
/**/

Description

Expands into a definition of a boolean unary Metafunction has_name such that for any type x has_name<x>::value == true if and only if x is a class type and has a nested type memeber x::name.

On the deficient compilers not capabale of performing the detection, has_name<x>::value always returns false. A boolean configuraion macro, BOOST_MPL_CFG_NO_HAS_XXX, is provided to signal or override the "deficient" status of a particular compiler.

[Note: BOOST_MPL_HAS_XXX_TRAIT_DEF is a simplified front end to the BOOST_MPL_HAS_XXX_TRAIT_NAMED_DEF introspection macro — end note]

Header

#include <boost/mpl/has_xxx.hpp>

Parameters

Expression semantics

For any legal C++ identifier name:

BOOST_MPL_HAS_XXX_TRAIT_DEF(name)

BOOST_MPL_HAS_XXX_TRAIT_NAMED_DEF(
      BOOST_PP_CAT(has_,name), name, false
    )

Example

BOOST_MPL_HAS_XXX_TRAIT_DEF(xxx)

struct test1 {};
struct test2 { void xxx(); };
struct test3 { int xxx; };
struct test4 { static int xxx(); };
struct test5 { template< typename T > struct xxx {}; };
struct test6 { typedef int xxx; };
struct test7 { struct xxx; };
struct test8 { typedef void (*xxx)(); };
struct test9 { typedef void (xxx)(); };

BOOST_MPL_ASSERT_NOT(( has_xxx<test1> ));
BOOST_MPL_ASSERT_NOT(( has_xxx<test2> ));
BOOST_MPL_ASSERT_NOT(( has_xxx<test3> ));
BOOST_MPL_ASSERT_NOT(( has_xxx<test4> ));
BOOST_MPL_ASSERT_NOT(( has_xxx<test5> ));

#if !defined(BOOST_MPL_CFG_NO_HAS_XXX)
BOOST_MPL_ASSERT(( has_xxx<test6> ));
BOOST_MPL_ASSERT(( has_xxx<test7> ));
BOOST_MPL_ASSERT(( has_xxx<test8> ));
BOOST_MPL_ASSERT(( has_xxx<test9> ));
#endif

BOOST_MPL_ASSERT(( has_xxx<test6,true_> ));
BOOST_MPL_ASSERT(( has_xxx<test7,true_> ));
BOOST_MPL_ASSERT(( has_xxx<test8,true_> ));
BOOST_MPL_ASSERT(( has_xxx<test9,true_> ));

See also

Macros, BOOST_MPL_HAS_XXX_TRAIT_NAMED_DEF, BOOST_MPL_CFG_NO_HAS_XXX