ceph/src/boost/libs/mpl/doc/src/refmanual/MetafunctionClass.rst

   1 .. Metafunctions/Concepts//Metafunction Class |20
   2
   3 Metafunction Class
   4 ==================
   5
   6 Summary
   7 -------
   8
   9 A *metafunction class* is a certain form of metafunction representation
  10 that enables higher-order metaprogramming. More precisely, it's a class
  11 with a publicly-accessible nested |metafunction| called ``apply``.
  12 Correspondingly, a metafunction class invocation is defined as invocation
  13 of its nested ``apply`` metafunction.
  14
  15
  16 Expression requirements
  17 -----------------------
  18
  19 |In the following table...| ``f`` is a |Metafunction Class|.
  20
  21 +-------------------------------+---------------------------+---------------------------+
  22 | Expression                    | Type                      | Complexity                |
  23 +===============================+===========================+===========================+
  24 | ``f::apply::type``            | Any type                  | Unspecified.              |
  25 +-------------------------------+---------------------------+---------------------------+
  26 | ``f::apply<>::type``          | Any type                  | Unspecified.              |
  27 +-------------------------------+---------------------------+---------------------------+
  28 | ``f::apply<a1,...an>::type``  | Any type                  | Unspecified.              |
  29 +-------------------------------+---------------------------+---------------------------+
  30
  31
  32 Expression semantics
  33 --------------------
  34
  35 .. parsed-literal::
  36
  37     typedef f::apply::type x;
  38
  39 :Precondition:
  40     ``f`` is a nullary |Metafunction Class|; ``f::apply::type`` is a *type-name*.
  41
  42 :Semantics:
  43     ``x`` is the result of the metafunction class invocation.
  44
  45
  46 .. ...................................................................................
  47
  48 .. parsed-literal::
  49
  50     typedef f::apply<>::type x;
  51
  52 :Precondition:
  53     ``f`` is a nullary |Metafunction Class|; ``f::apply<>::type`` is a *type-name*.
  54
  55 :Semantics:
  56     ``x`` is the result of the metafunction class invocation.
  57
  58
  59 .. ...................................................................................
  60
  61 .. parsed-literal::
  62
  63     typedef f::apply<a1,\ |...|\ a\ *n*\>::type x;
  64
  65 :Precondition:
  66     ``f`` is an *n*-ary metafunction class; ``apply`` is a |Metafunction|.
  67
  68 :Semantics:
  69     ``x`` is the result of the metafunction class
  70     invocation with the actual arguments |a1...an|.
  71
  72
  73 Models
  74 ------
  75
  76 * |always|
  77 * |arg|
  78 * |quote|
  79 * |numeric_cast|
  80 * |unpack_args|
  81
  82
  83 See also
  84 --------
  85
  86 |Metafunctions|, |Metafunction|, |Lambda Expression|, |Invocation|, |apply_wrap|, |bind|, |quote|
  87
  88
  89 .. copyright:: Copyright ©  2001-2009 Aleksey Gurtovoy and David Abrahams
  90    Distributed under the Boost Software License, Version 1.0. (See accompanying
  91    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)