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converts_to.hh
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25 
26 #ifndef MLN_METAL_CONVERTS_TO_HH
27 # define MLN_METAL_CONVERTS_TO_HH
28 
33 
34 # include <mln/metal/is_a.hh>
35 # include <mln/metal/const.hh>
36 # include <mln/core/def/coord.hh>
37 
38 
39 # define mlc_converts_to(T, U) mln::metal::converts_to< T, U >
40 
41 
42 
43 namespace mln
44 {
45 
46  // Forward declarations.
47  namespace value {
48  template <unsigned n> struct int_u;
49  template <unsigned n> struct int_s;
50  }
51 
52 
53  namespace metal
54  {
55 
56  namespace internal
57  {
58 
59  struct eat // Required by g++-2.95 for selector to work.
60  {
61  template <typename T> eat(const volatile T&);
62  template <typename T> eat(T&);
63  };
64 
65  template <typename T, typename U>
66  struct helper_converts_to_
67  {
68  static yes_ selector(U, int);
69  static no_ selector(eat, ...);
70  };
71 
72  } // end of namespace mln::metal::internal
73 
74 
75 
77  template <typename T, typename U>
78  struct converts_to : bool_<( sizeof(internal::helper_converts_to_<T, U>
79  ::selector(*internal::make_<mlc_const(T)>::ptr(),
80  0) )
81  ==
82  sizeof(internal::yes_) )>
83  {};
84 
85 
86  template <typename T, typename U>
87  struct converts_to<T*, U*> : converts_to<T, U>
88  {};
89 
90  template <typename T, typename U>
91  struct converts_to<T**, U**> : false_
92  {};
93 
94 
95 
96  // Below, a few hacks to quiet g++-3.4 warnings:
97 
98  template <> struct converts_to< float, int > : true_ {};
99  template <> struct converts_to< float, def::coord > : true_ {};
100  template <unsigned n> struct converts_to< float, value::int_u<n> > : true_ {};
101  template <unsigned n> struct converts_to< float, value::int_s<n> > : true_ {};
102 
103  template <> struct converts_to< double, int > : true_ {};
104  template <> struct converts_to< double, def::coord > : true_ {};
105  template <unsigned n> struct converts_to< double, value::int_u<n> > : true_ {};
106  template <unsigned n> struct converts_to< double, value::int_s<n> > : true_ {};
107 
108  // End of hacks.
109 
110  } // end of namespace mln::metal
111 
112 
113 
114 } // end of namespace mln
115 
116 
117 #endif // ! MLN_METAL_CONVERTS_TO_HH