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1 | .. Macros/Configuration//BOOST_MPL_LIMIT_METAFUNCTION_ARITY |20 |
| 2 | ||
| 3 | BOOST_MPL_LIMIT_METAFUNCTION_ARITY | |
| 4 | ================================== | |
| 5 | ||
| 6 | Synopsis | |
| 7 | -------- | |
| 8 | ||
| 9 | .. parsed-literal:: | |
| 10 | ||
| 11 | #if !defined(BOOST_MPL_LIMIT_METAFUNCTION_ARITY) | |
| 12 | # define BOOST_MPL_LIMIT_METAFUNCTION_ARITY \\ | |
| 13 | |idic| \\ | |
| 14 | /\*\*/ | |
| 15 | #endif | |
| 16 | ||
| 17 | ||
| 18 | Description | |
| 19 | ----------- | |
| 20 | ||
| 21 | ``BOOST_MPL_LIMIT_METAFUNCTION_ARITY`` is an overridable configuration macro | |
| 22 | regulating the maximum supported arity of `metafunctions`__ and | |
| 23 | `metafunction classes`__. In this implementation of the | |
| 24 | library, ``BOOST_MPL_LIMIT_METAFUNCTION_ARITY`` has a default value of 5. To | |
| 25 | override the default limit, define ``BOOST_MPL_LIMIT_METAFUNCTION_ARITY`` to | |
| 26 | the desired maximum arity before including any library header. | |
| 27 | |preprocessed headers disclaimer| | |
| 28 | ||
| 29 | __ `Metafunction`_ | |
| 30 | __ `Metafunction Class`_ | |
| 31 | ||
| 32 | ||
| 33 | Example | |
| 34 | ------- | |
| 35 | ||
| 36 | .. parsed-literal:: | |
| 37 | ||
| 38 | #define BOOST_MPL_CFG_NO_PREPROCESSED_HEADERS | |
| 39 | #define BOOST_MPL_LIMIT_METAFUNCTION_ARITY 2 | |
| 40 | ``#``\ include <boost/mpl/apply.hpp> | |
| 41 | ||
| 42 | using namespace boost::mpl; | |
| 43 | ||
| 44 | template< typename T1, typename T2 > struct second | |
| 45 | { | |
| 46 | typedef T2 type; | |
| 47 | }; | |
| 48 | ||
| 49 | template< typename T1, typename T2, typename T3 > struct third | |
| 50 | { | |
| 51 | typedef T3 type; | |
| 52 | }; | |
| 53 | ||
| 54 | typedef apply< second<_1,_2_>,int,long >::type r1; | |
| 55 | // typedef apply< third<_1,_2_,_3>,int,long,float >::type r2; // error! | |
| 56 | ||
| 57 | ||
| 58 | See also | |
| 59 | -------- | |
| 60 | ||
| 61 | |Macros|, |Configuration|, |BOOST_MPL_CFG_NO_PREPROCESSED_HEADERS| | |
| 62 | ||
| 63 | ||
| 64 |