ceph/src/boost/libs/tti/doc/tti_using_mm.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_usingMM An example using the Macro Metafunctions]
   9 [#sectti_usingMM]
  10
  11 Using the macro metafunctions can be illustrated by first creating some hypothetical
  12 user-defined type with corresponding nested types and other inner elements.
  13 With this type we can illustrate the use of the macro metafunctions. This is
  14 just meant to serve as a model for what a type T might entail from within
  15 a class or function template where 'T' is a type passed to the template.
  16
  17  // An enclosing type
  18
  19  struct AType
  20    {
  21
  22    // Type
  23
  24    typedef int AnIntType; // as a typedef
  25
  26    struct BType // as a nested type
  27      {
  28      struct CType
  29        {
  30        };
  31      };
  32
  33    // Template
  34
  35    template <class> struct AMemberTemplate { };
  36    template <class,class,class> struct AnotherMemberTemplate { };
  37    template <class,class,int,class,template <class> class,class,long> struct ManyParameters { };
  38    template <class,class,int,short,class,template <class,int> class,class> struct MoreParameters { };
  39
  40    // Data
  41
  42    BType IntBT;
  43
  44    // Function
  45
  46    int IntFunction(short) { return 0; }
  47
  48    // Static Data
  49
  50    static short DSMember;
  51
  52    // Static Function
  53
  54    static int SIntFunction(long,double) { return 2; }
  55
  56    };
  57
  58 I will be using the type above just to illustrate the sort of
  59 metaprogramming questions we can ask of some type T which is passed
  60 to the template programmer in a class template. Here is what the
  61 class template might look like:
  62
  63  #include <boost/tti/tti.hpp>
  64
  65  template<class T>
  66  struct OurTemplateClass
  67    {
  68
  69    // compile-time template code regarding T
  70
  71    };
  72
  73 Now let us create and invoke the macro metafunctions for each of our inner element types,
  74 to see if type T above corresponds to our hypothetical type above. Imagine this being
  75 within 'OurTemplateClass' above. In the examples below the same macro is invoked just once
  76 to avoid ODR violations.
  77
  78 [heading Type]
  79
  80 Does T have a nested type called 'AnIntType' ?
  81
  82  BOOST_TTI_HAS_TYPE(AnIntType)
  83
  84  has_type_AnIntType
  85    <
  86    T
  87    >
  88
  89 Does T have a nested type called 'BType' ?
  90
  91  BOOST_TTI_HAS_TYPE(BType)
  92
  93  has_type_BType
  94    <
  95    T
  96    >
  97
  98 [heading Type checking the typedef using a lambda expression]
  99
 100 Does T have a nested typedef called 'AnIntType' whose type is an 'int' ?
 101
 102  #include <boost/mpl/placeholders.hpp
 103  #include <boost/type_traits/is_same.hpp
 104  using namespace boost::mpl::placeholders;
 105
 106  has_type_AnIntType
 107    <
 108    T,
 109    boost::is_same<_1,int>
 110    >
 111
 112 [heading Template]
 113
 114 Does T have a nested class template called 'AMemberTemplate' whose template
 115 parameters are all types ('class' or 'typename') ?
 116
 117  BOOST_TTI_HAS_TEMPLATE(AMemberTemplate,BOOST_PP_NIL)
 118
 119  has_template_AMemberTemplate
 120    <
 121    T
 122    >
 123
 124 [heading Template using variadic macros]
 125
 126 Does T have a nested class template called 'AMemberTemplate' whose template
 127 parameters are all types ('class' or 'typename') ?
 128
 129  BOOST_TTI_HAS_TEMPLATE(AnotherMemberTemplate)
 130
 131  has_template_AnotherMemberTemplate
 132    <
 133    T
 134    >
 135
 136 [heading Template with params]
 137
 138 Does T have a nested class template called 'MoreParameters' whose template
 139 parameters are specified exactly ?
 140
 141  BOOST_TTI_HAS_TEMPLATE(MoreParameters,(8,(class,class,int,short,class,template <class,int> class,class)))
 142
 143  has_template_MoreParameters
 144    <
 145    T
 146    >
 147
 148 [heading Template with params using variadic macros]
 149
 150 Does T have a nested class template called 'ManyParameters' whose template
 151 parameters are specified exactly ?
 152
 153  BOOST_TTI_HAS_TEMPLATE(ManyParameters,class,class,int,class,template <class> class,class,long)
 154
 155  has_template_ManyParameters
 156    <
 157    T
 158    >
 159
 160 [heading Member data]
 161
 162 Does T have a member data called 'IntBT' whose type is 'AType::BType' ?
 163
 164  BOOST_TTI_HAS_MEMBER_DATA(IntBT)
 165
 166  has_member_data_IntBT
 167    <
 168    T,
 169    AType::BType
 170    >
 171
 172 [heading Member data with composite type]
 173
 174 Does T have a member data called 'IntBT' whose type is 'AType::BType' ?
 175
 176  BOOST_TTI_HAS_MEMBER_DATA(IntBT)
 177
 178  has_member_data_IntBT
 179    <
 180    AType::BType T::*
 181    >
 182
 183 [heading Member function with individual types]
 184
 185 Does T have a member function called 'IntFunction' whose type is
 186 'int (short)' ?
 187
 188  BOOST_TTI_HAS_MEMBER_FUNCTION(IntFunction)
 189
 190  has_member_function_IntFunction
 191    <
 192    T,
 193    int,
 194    boost::mpl::vector<short>
 195    >
 196
 197 [heading Member function with composite type]
 198
 199 Does T have a member function called 'IntFunction' whose type is
 200 'int (short)' ?
 201
 202  BOOST_TTI_HAS_MEMBER_FUNCTION(IntFunction)
 203  has_member_function_IntFunction
 204    <
 205    int (T::*)(short)
 206    >
 207
 208 [heading Static member data]
 209
 210 Does T have a static member data called 'DSMember' whose type is 'short' ?
 211
 212  BOOST_TTI_HAS_STATIC_MEMBER_DATA(DSMember)
 213
 214  has_static_member_data_DSMember
 215    <
 216    T,
 217    short
 218    >
 219
 220 [heading Static member function with individual types]
 221
 222 Does T have a static member function called 'SIntFunction' whose type
 223 is 'int (long,double)' ?
 224
 225  BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION(SIntFunction)
 226
 227  has_static_member_function_SIntFunction
 228    <
 229    T,
 230    int,
 231    boost::mpl::vector<long,double>
 232    >
 233
 234 [heading Static member function with composite type]
 235
 236 Does T have a static member function called 'SIntFunction' whose type
 237 is 'int (long,double)' ?
 238
 239  BOOST_TTI_HAS_STATIC_MEMBER_FUNCTION(SIntFunction)
 240
 241  has_static_member_function_SIntFunction
 242    <
 243    T,
 244    int (long,double)
 245    >
 246
 247 [heading Data]
 248
 249 Does T have a member data or static member data called 'DSMember' whose type is 'short' ?
 250
 251  BOOST_TTI_HAS_DATA(DSMember)
 252
 253  has_static_member_data_DSMember
 254    <
 255    T,
 256    short
 257    >
 258
 259 [heading Function]
 260
 261 Does T have a member function or a static member function called 'IntFunction' whose type is
 262 'int (short)' ?
 263
 264  BOOST_TTI_HAS_FUNCTION(IntFunction)
 265
 266  has_function_IntFunction
 267    <
 268    T,
 269    int,
 270    boost::mpl::vector<short>
 271    >
 272
 273 [heading Member type]
 274
 275 Create a nested type T::BType::CType without creating a compiler error
 276 if T does not have the nested type BType::CType ?
 277
 278  BOOST_TTI_MEMBER_TYPE(BType)
 279  BOOST_TTI_MEMBER_TYPE(CType)
 280
 281  typename
 282  member_type_CType
 283    <
 284    typename
 285    member_type_BType
 286      <
 287      T
 288      >::type
 289    >::type
 290
 291 [heading Member type existence]
 292
 293 Does a nested type T::BType::CType, created without creating a compiler error
 294 if T does not have the nested type BType::CType, actually exist ?
 295
 296  BOOST_TTI_MEMBER_TYPE(BType)
 297  BOOST_TTI_MEMBER_TYPE(CType)
 298
 299  typedef typename
 300  member_type_CType
 301    <
 302    typename
 303    member_type_BType
 304      <
 305      T
 306      >::type
 307    >::type
 308  AType;
 309
 310  boost::tti::valid_member_type
 311    <
 312    AType
 313    >
 314
 315 [endsect]