ceph/src/boost/libs/config/test/boost_no_decltype_n3276.ipp

   1
   2 //  (C) Copyright Eric Niebler 2011
   3
   4 //  Use, modification and distribution are subject to the
   5 //  Boost Software License, Version 1.0. (See accompanying file
   6 //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   7
   8 //  See http://www.boost.org/libs/config for more information.
   9
  10 //  MACRO:         BOOST_NO_CXX11_DECLTYPE_N3276
  11 //  TITLE:         C++0x decltype v1.1 unavailable
  12 //  DESCRIPTION:   The compiler does not support extensions to C++0x
  13 //                 decltype as described in N3276 and accepted in Madrid,
  14 //                 March 2011:
  15 //                 <http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3276.pdf>
  16
  17 namespace boost_no_cxx11_decltype_n3276 {
  18
  19 // A simplified result_of implementation.
  20 // that uses decltype.
  21 template<typename Sig>
  22 struct result_of;
  23
  24 template<typename T>
  25 T& declvar();
  26
  27 // use decltype
  28 template<typename Fun, typename T>
  29 struct result_of<Fun(T)>
  30 {
  31     typedef decltype(declvar<Fun>()(declvar<T>())) type;
  32 };
  33
  34 template<typename Fun, typename T, typename U>
  35 struct result_of<Fun(T, U)>
  36 {
  37     typedef decltype(declvar<Fun>()(declvar<T>(), declvar<U>())) type;
  38 };
  39
  40 // simple tuple type
  41 template<typename A0 = void, typename A1 = void, typename A2 = void>
  42 struct tuple;
  43
  44 template<typename A0>
  45 struct tuple<A0, void, void>
  46 {
  47     A0 a0_;
  48
  49     tuple(A0 const &a0)
  50       : a0_(a0)
  51     {}
  52 };
  53
  54 template<typename A0, typename A1>
  55 struct tuple<A0, A1>
  56 {
  57     A0 a0_;
  58     A1 a1_;
  59
  60     tuple(A0 const &a0, A1 const & a1)
  61       : a0_(a0)
  62       , a1_(a1)
  63     {}
  64 };
  65
  66 // A node in an expression tree
  67 template<class Tag, class Args> // Args is a tuple.
  68 struct Expr;
  69
  70 // A function object that builds expression nodes
  71 template<class Tag>
  72 struct MakeExpr
  73 {
  74     template<class T>
  75     Expr<Tag, tuple<T> > operator()(T const & t) const
  76     {
  77         return Expr<Tag, tuple<T> >(tuple<T>(t));
  78     }
  79
  80     template<class T, typename U>
  81     Expr<Tag, tuple<T, U> > operator()(T const & t, U const & u) const
  82     {
  83         return Expr<Tag, tuple<T, U> >(tuple<T, U>(t, u));
  84     }
  85 };
  86
  87 // Here are tag types that encode in an expression node
  88 // what operation created the node.
  89 struct Terminal;
  90 struct BinaryPlus;
  91 struct FunctionCall;
  92
  93 typedef MakeExpr<Terminal> MakeTerminal;
  94 typedef MakeExpr<BinaryPlus> MakeBinaryPlus;
  95 typedef MakeExpr<FunctionCall> MakeFunctionCall;
  96
  97 template<class Tag, class Args>
  98 struct Expr
  99 {
 100     Args args_;
 101
 102     explicit Expr(Args const & t) : args_(t) {}
 103
 104     // An overloaded operator+ that creates a binary plus node
 105     template<typename RTag, typename RArgs>
 106     typename result_of<MakeBinaryPlus(Expr, Expr<RTag, RArgs>)>::type
 107     operator+(Expr<RTag, RArgs> const &right) const
 108     {
 109         return MakeBinaryPlus()(*this, right);
 110     }
 111
 112     // An overloaded function call operator that creates a unary
 113     // function call node
 114     typename result_of<MakeFunctionCall(Expr)>::type
 115     operator()() const
 116     {
 117         return MakeFunctionCall()(*this);
 118     }
 119 };
 120
 121 int test()
 122 {
 123     // This is a terminal in an expression tree
 124     Expr<Terminal, tuple<int> > i = MakeTerminal()(42);
 125
 126     i + i; // OK, this creates a binary plus node.
 127
 128     i(); // OK, this creates a unary function-call node.
 129          // NOTE: If N3276 has not been implemented, this
 130          // line will set off an infinite cascade of template
 131          // instantiations that will run the compiler out of
 132          // memory.
 133
 134     return 0;
 135 }
 136
 137 }