1 | // (C) Copyright Jonathan Turkanis 2004.
|
---|
2 | // Distributed under the Boost Software License, Version 1.0. (See accompanying
|
---|
3 | // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt.)
|
---|
4 |
|
---|
5 | // See http://www.boost.org/libs/iostreams for documentation.
|
---|
6 |
|
---|
7 | //
|
---|
8 | // Intended as an alternative to type_traits::yes_type and type_traits::no_type.
|
---|
9 | // Provides an arbitrary number of types (case_<0>, case_<1>, ...) for
|
---|
10 | // determining the results of overload resultion using 'sizeof', plus a uniform
|
---|
11 | // means of using the result. yes_type and no_type are typedefs for case_<1>
|
---|
12 | // and case_<0>. A single case with negative argument, case_<-1>, is also
|
---|
13 | // provided, for convenience.
|
---|
14 | //
|
---|
15 | // This header may be included any number of times, with
|
---|
16 | // BOOST_SELECT_BY_SIZE_MAX_CASE defined to be the largest N such that case_<N>
|
---|
17 | // is needed for a particular application. It defaults to 20.
|
---|
18 | //
|
---|
19 | // This header depends only on Boost.Config and Boost.Preprocessor. Dependence
|
---|
20 | // on Type Traits or MPL was intentionally avoided, to leave open the
|
---|
21 | // possibility that select_by_size could be used by these libraries.
|
---|
22 | //
|
---|
23 | // Example usage:
|
---|
24 | //
|
---|
25 | // #define BOOST_SELECT_BY_SIZE_MAX_CASE 7 // (Needed when default was 2)
|
---|
26 | // #include <boost/utility/select_by_size.hpp>
|
---|
27 | //
|
---|
28 | // using namespace boost::utility;
|
---|
29 | //
|
---|
30 | // case_<0> helper(bool);
|
---|
31 | // case_<1> helper(int);
|
---|
32 | // case_<2> helper(unsigned);
|
---|
33 | // case_<3> helper(long);
|
---|
34 | // case_<4> helper(unsigned long);
|
---|
35 | // case_<5> helper(float);
|
---|
36 | // case_<6> helper(double);
|
---|
37 | // case_<7> helper(const char*);
|
---|
38 | //
|
---|
39 | // struct test {
|
---|
40 | // static const int value =
|
---|
41 | // select_by_size< sizeof(helper(9876UL)) >::value;
|
---|
42 | // BOOST_STATIC_ASSERT(value == 4);
|
---|
43 | // };
|
---|
44 | //
|
---|
45 | // For compilers with integral constant expression problems, e.g. Borland 5.x,
|
---|
46 | // one can also write
|
---|
47 | //
|
---|
48 | // struct test {
|
---|
49 | // BOOST_SELECT_BY_SIZE(int, value, helper(9876UL));
|
---|
50 | // };
|
---|
51 | //
|
---|
52 | // to define a static integral constant 'value' equal to
|
---|
53 | //
|
---|
54 | // select_by_size< sizeof(helper(9876UL)) >::value.
|
---|
55 | //
|
---|
56 |
|
---|
57 | // Include guards surround all contents of this header except for explicit
|
---|
58 | // specializations of select_by_size for case_<N> with N > 2.
|
---|
59 |
|
---|
60 | #ifndef BOOST_IOSTREAMS_DETAIL_SELECT_BY_SIZE_HPP_INCLUDED
|
---|
61 | #define BOOST_IOSTREAMS_DETAIL_SELECT_BY_SIZE_HPP_INCLUDED
|
---|
62 |
|
---|
63 | // The lowest N for which select_by_size< sizeof(case_<N>) > has not been
|
---|
64 | // specialized.
|
---|
65 | #define SELECT_BY_SIZE_MAX_SPECIALIZED 20
|
---|
66 |
|
---|
67 | #include <boost/config.hpp> // BOOST_STATIC_CONSTANT.
|
---|
68 | #include <boost/preprocessor/cat.hpp>
|
---|
69 | #include <boost/preprocessor/iteration/local.hpp>
|
---|
70 |
|
---|
71 | /* Alternative implementation using max_align.
|
---|
72 |
|
---|
73 | #include <boost/type_traits/alignment_of.hpp>
|
---|
74 | #include <boost/type_traits/type_with_alignment.hpp>
|
---|
75 |
|
---|
76 | namespace boost { namespace utility {
|
---|
77 |
|
---|
78 | template<int N>
|
---|
79 | struct case_ { char c[(N + 1) * alignment_of<detail::max_align>::value]; };
|
---|
80 |
|
---|
81 | template<unsigned Size>
|
---|
82 | struct select_by_size {
|
---|
83 | BOOST_STATIC_CONSTANT(int, value =
|
---|
84 | (Size / alignment_of<detail::max_align>::value - 1));
|
---|
85 | };
|
---|
86 |
|
---|
87 | } } // End namespaces utility, boost.
|
---|
88 |
|
---|
89 | */ // End alternate implementation.
|
---|
90 |
|
---|
91 | namespace boost { namespace iostreams { namespace detail {
|
---|
92 |
|
---|
93 | //--------------Definition of case_-------------------------------------------//
|
---|
94 |
|
---|
95 | template<int N> struct case_ { char c1; case_<N - 1> c2; };
|
---|
96 | template<> struct case_<-1> { char c; };
|
---|
97 | typedef case_<true> yes_type;
|
---|
98 | typedef case_<false> no_type;
|
---|
99 |
|
---|
100 | //--------------Declaration of select_by_size---------------------------------//
|
---|
101 |
|
---|
102 | template<unsigned Size> struct select_by_size;
|
---|
103 |
|
---|
104 | } } } // End namespaces detail, iostreams, boost.
|
---|
105 |
|
---|
106 | //--------------Definition of SELECT_BY_SIZE_SPEC-----------------------------//
|
---|
107 |
|
---|
108 | // Sepecializes select_by_size for sizeof(case<n-1>). The decrement is used
|
---|
109 | // here because the preprocessor library doesn't handle negative integers.
|
---|
110 | #define SELECT_BY_SIZE_SPEC(n) \
|
---|
111 | namespace boost { namespace iostreams { namespace detail { \
|
---|
112 | static const int BOOST_PP_CAT(sizeof_case_, n) = sizeof(case_<n - 1>); \
|
---|
113 | template<> \
|
---|
114 | struct select_by_size< BOOST_PP_CAT(sizeof_case_, n) > { \
|
---|
115 | struct type { BOOST_STATIC_CONSTANT(int, value = n - 1); }; \
|
---|
116 | BOOST_STATIC_CONSTANT(int, value = type::value); \
|
---|
117 | }; \
|
---|
118 | } } } \
|
---|
119 | /**/
|
---|
120 |
|
---|
121 | //--------------Default specializations of select_by_size---------------------//
|
---|
122 |
|
---|
123 | #define BOOST_PP_LOCAL_MACRO(n) SELECT_BY_SIZE_SPEC(n)
|
---|
124 | #define BOOST_PP_LOCAL_LIMITS (0, 20)
|
---|
125 | #include BOOST_PP_LOCAL_ITERATE()
|
---|
126 | #undef BOOST_PP_LOCAL_MACRO
|
---|
127 |
|
---|
128 | //--------------Definition of SELECT_BY_SIZE----------------------------------//
|
---|
129 |
|
---|
130 | #define BOOST_SELECT_BY_SIZE(type_, name, expr) \
|
---|
131 | BOOST_STATIC_CONSTANT( \
|
---|
132 | unsigned, \
|
---|
133 | BOOST_PP_CAT(boost_select_by_size_temp_, name) = sizeof(expr) \
|
---|
134 | ); \
|
---|
135 | BOOST_STATIC_CONSTANT( \
|
---|
136 | type_, \
|
---|
137 | name = \
|
---|
138 | ( ::boost::iostreams::detail::select_by_size< \
|
---|
139 | BOOST_PP_CAT(boost_select_by_size_temp_, name) \
|
---|
140 | >::value ) \
|
---|
141 | ) \
|
---|
142 | /**/
|
---|
143 |
|
---|
144 | #endif // #ifndef BOOST_IOSTREAMS_DETAIL_SELECT_BY_SIZE_HPP_INCLUDED
|
---|
145 |
|
---|
146 | //----------Specializations of SELECT_BY_SIZE (outside main inclued guards)---//
|
---|
147 |
|
---|
148 | #if BOOST_SELECT_BY_SIZE_MAX_CASE > SELECT_BY_SIZE_MAX_SPECIALIZED
|
---|
149 |
|
---|
150 | #define BOOST_PP_LOCAL_MACRO(n) SELECT_BY_SIZE_SPEC(n)
|
---|
151 | #define BOOST_PP_LOCAL_LIMITS \
|
---|
152 | (SELECT_BY_SIZE_MAX_SPECIALIZED, BOOST_SELECT_BY_SIZE_MAX_CASE) \
|
---|
153 | /**/
|
---|
154 | #include BOOST_PP_LOCAL_ITERATE()
|
---|
155 | #undef BOOST_PP_LOCAL_MACRO
|
---|
156 | #undef SELECT_BY_SIZE_MAX_SPECIALIZED
|
---|
157 | #define SELECT_BY_SIZE_MAX_SPECIALIZED BOOST_SELECT_BY_SIZE_MAX_CASE
|
---|
158 |
|
---|
159 | #endif
|
---|