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1 | // (C) Copyright David Abrahams 2002. |
2 | // (C) Copyright Jeremy Siek 2002. | |
3 | // (C) Copyright Thomas Witt 2002. | |
4 | // Distributed under the Boost Software License, Version 1.0. (See | |
5 | // accompanying file LICENSE_1_0.txt or copy at | |
6 | // http://www.boost.org/LICENSE_1_0.txt) | |
7 | #ifndef BOOST_ENABLE_IF_23022003THW_HPP | |
8 | #define BOOST_ENABLE_IF_23022003THW_HPP | |
9 | ||
10 | #include <boost/detail/workaround.hpp> | |
11 | #include <boost/mpl/identity.hpp> | |
12 | ||
13 | #include <boost/iterator/detail/config_def.hpp> | |
14 | ||
15 | // | |
16 | // Boost iterators uses its own enable_if cause we need | |
17 | // special semantics for deficient compilers. | |
18 | // 23/02/03 thw | |
19 | // | |
20 | ||
21 | namespace boost | |
22 | { | |
23 | ||
24 | namespace iterators | |
25 | { | |
26 | // | |
27 | // Base machinery for all kinds of enable if | |
28 | // | |
29 | template<bool> | |
30 | struct enabled | |
31 | { | |
32 | template<typename T> | |
33 | struct base | |
34 | { | |
35 | typedef T type; | |
36 | }; | |
37 | }; | |
38 | ||
39 | // | |
40 | // For compilers that don't support "Substitution Failure Is Not An Error" | |
41 | // enable_if falls back to always enabled. See comments | |
42 | // on operator implementation for consequences. | |
43 | // | |
44 | template<> | |
45 | struct enabled<false> | |
46 | { | |
47 | template<typename T> | |
48 | struct base | |
49 | { | |
50 | #ifdef BOOST_NO_SFINAE | |
51 | ||
52 | typedef T type; | |
53 | ||
54 | // This way to do it would give a nice error message containing | |
55 | // invalid overload, but has the big disadvantage that | |
56 | // there is no reference to user code in the error message. | |
57 | // | |
58 | // struct invalid_overload; | |
59 | // typedef invalid_overload type; | |
60 | // | |
61 | #endif | |
62 | }; | |
63 | }; | |
64 | ||
65 | ||
66 | template <class Cond, | |
67 | class Return> | |
68 | struct enable_if | |
69 | # if !defined(BOOST_NO_SFINAE) && !defined(BOOST_NO_IS_CONVERTIBLE) | |
70 | : enabled<(Cond::value)>::template base<Return> | |
71 | # else | |
72 | : mpl::identity<Return> | |
73 | # endif | |
74 | { | |
75 | }; | |
76 | ||
77 | } // namespace iterators | |
78 | ||
79 | } // namespace boost | |
80 | ||
81 | #include <boost/iterator/detail/config_undef.hpp> | |
82 | ||
83 | #endif // BOOST_ENABLE_IF_23022003THW_HPP |