ceph/src/boost/libs/tti/doc/tti_detail_has_static_member_function.qbk

   1 [/
   2   (C) Copyright Edward Diener 2011,2012
   3   Distributed under the Boost Software License, Version 1.0.
   4   (See accompanying file LICENSE_1_0.txt or copy at
   5   http://www.boost.org/LICENSE_1_0.txt).
   6 ]
   7
   8 [section:tti_detail_has_static_member_function Introspecting static member function]
   9
  10 The TTI macro [macroref BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION] introspects
  11 a static member function of a class.
  12
  13 BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION takes a single
  14 parameter which is the name of an inner static member function whose existence
  15 the programmer wants to check. The macro generates a metafunction
  16 called 'has_static_member_function_'name_of_inner_static_member_function'.
  17
  18 The metafunction can be invoked in two different ways.
  19
  20 The first way is by passing it the enclosing type to introspect and a
  21 signature for the static member function as separate template
  22 arguments. The signature for the static member function consists of a return
  23 type, optional parameter types in the form of a boost::mpl forward
  24 sequence of types, and an optional Boost FunctionTypes tag type. A
  25 typical boost::mpl forward sequence of types is a boost::mpl::vector<>.
  26
  27 The second way is by passing it the enclosing type to introspect and a
  28 signature for the static member function as a function. The function
  29 has the form of:
  30
  31  Return_Type ( Parameter_Types )
  32
  33 where the Parameter_Types may be empty, or a comma-separated
  34 list of parameter types if there are more than one parameter type.
  35
  36 The metafunction returns a single type called 'type', which is a
  37 boost::mpl::bool_. As a convenience the metafunction
  38 returns the value of this type directly as a compile time bool constant
  39 called 'value'. This is true or false depending on whether the inner
  40 static member function, of the specified signature, exists or not.
  41
  42 [heading Generating the metafunction]
  43
  44 You generate the metafunction by invoking the macro with the name
  45 of an inner static member function:
  46
  47   BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION(AStaticMemberFunction)
  48
  49 generates a metafunction called 'has_static_member_function_AStaticMemberFunction' in the current scope.
  50
  51 [heading Invoking the metafunction]
  52
  53 You invoke the metafunction by instantiating the template with an enclosing
  54 type to introspect and the signature of the static member function as a series of template
  55 parameters. Alternatively you can invoke the metafunction by passing it an enclosing type
  56 and the signature of the static member function as a single function type.
  57
  58 A return value called 'value' is a compile time bool constant.
  59
  60   has_static_member_function_AStaticMemberFunction
  61     <
  62     Enclosing_Type,
  63     StaticMemberFunction_ReturnType,
  64     boost::mpl::vector<StaticMemberFunction_ParameterTypes>, // optional, can be any mpl forward sequence
  65     boost::function_types::SomeTagType                       // optional, can be any FunctionTypes tag type
  66     >::value
  67
  68   OR
  69
  70   has_static_member_function_AStaticMemberFunction
  71     <
  72     Enclosing_Type,
  73     Return_Type ( Parameter_Types )
  74     >::value
  75
  76 [heading Examples]
  77
  78 First we generate metafunctions for various inner static member function names:
  79
  80  #include <boost/tti/has_static_member_function.hpp>
  81
  82  BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION(function1)
  83  BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION(function2)
  84  BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION(function3)
  85
  86 Next let us create some user-defined types we want to introspect.
  87
  88  struct AClass { };
  89  struct Top
  90    {
  91    static int function1();
  92    static AClass function2(double,short *);
  93    };
  94  struct Top2
  95    {
  96    static long function2(Top &,int,bool,short,float);
  97    static Top * function3(long,int,AClass &);
  98    };
  99
 100 Finally we invoke our metafunction and return our value.
 101 This all happens at compile time, and can be used by
 102 programmers doing compile time template metaprogramming.
 103
 104 We will show both forms in the following examples.
 105 Both forms are completely interchangeable as to the result
 106 desired.
 107
 108  has_static_member_function_function1<Top,int>::value; // true
 109  has_static_member_function_function1<Top,int ()>::value; // true
 110  has_static_member_function_function1<Top2,int>::value; // false
 111
 112  has_static_member_function_function2<Top,AClass,boost::mpl::vector<double,short *> >::value; // true
 113  has_static_member_function_function2<Top2,AClass,boost::mpl::vector<double,short *> >::value; // false
 114  has_static_member_function_function2<Top2,long (Top &,int,bool,short,float)>::value; // true
 115
 116  has_static_member_function_function3<Top2,int ()>::value; // false
 117  has_static_member_function_function3<Top2,Top * (long,int,AClass &)>::value; // true;
 118
 119 [heading Metafunction re-use]
 120
 121 The macro encodes only the name of the static member function
 122 for which we are searching and the fact that we are
 123 introspecting for a static member function within an enclosing type.
 124
 125 Because of this, once we create our metafunction for
 126 introspecting a static member function by name, we can reuse the
 127 metafunction for introspecting any enclosing type, having any
 128 static member function, for that name.
 129
 130 [endsect]