The MPL Reference Manual: BOOST_MPL_HAS_XXX_TEMPLATE_DEF

Front Page / Macros / Introspection / BOOST_MPL_HAS_XXX_TEMPLATE_DEF

# BOOST_MPL_HAS_XXX_TEMPLATE_DEF

### Synopsis

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

### Description

Expands into the definition of a boolean 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 template member `x::template name` with no more than BOOST_MPL_LIMIT_METAFUNCTION_ARITY parameters.

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

[Note: BOOST_MPL_HAS_XXX_TEMPLATE_DEF is a simplified front end to the BOOST_MPL_HAS_XXX_TEMPLATE_NAMED_DEF introspection macro — end note]

### Header

    #include <boost/mpl/has_xxx.hpp>

### Parameters

Parameter | Requirement | Description
--- | --- | ---
`name` | A legal identifier token | A name of the template member being detected.

### Expression semantics

For any legal C++ identifier `name`:

    BOOST_MPL_HAS_XXX_TEMPLATE_DEF(name)

Precondition: | Appears at namespace scope.
Return type: | None.
Semantics: | Equivalent to
    BOOST_MPL_HAS_XXX_TEMPLATE_NAMED_DEF(
          BOOST_PP_CAT(has_,name), name, false
        )

### Example

    BOOST_MPL_HAS_XXX_TEMPLATE_DEF(xxx)

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

    #if !defined(BOOST_MPL_CFG_NO_HAS_XXX_TEMPLATE)
    BOOST_MPL_ASSERT(( has_xxx<test9> ));
    #endif

    BOOST_MPL_ASSERT(( has_xxx<test9, true_> ));

### See also

Macros, BOOST_MPL_HAS_XXX_TEMPLATE_NAMED_DEF, BOOST_MPL_CFG_NO_HAS_XXX_TEMPLATE, BOOST_MPL_LIMIT_METAFUNCTION_ARITY