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1 | // Copyright Daniel Wallin 2006. Use, modification and distribution is |
2 | // subject to 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 | #ifndef BOOST_PARAMETER_VALUE_TYPE_060921_HPP | |
6 | # define BOOST_PARAMETER_VALUE_TYPE_060921_HPP | |
7 | ||
8 | # include <boost/mpl/apply.hpp> | |
9 | # include <boost/mpl/assert.hpp> | |
10 | # include <boost/mpl/and.hpp> | |
11 | # include <boost/parameter/aux_/result_of0.hpp> | |
12 | # include <boost/parameter/aux_/void.hpp> | |
13 | # include <boost/type_traits/is_same.hpp> | |
14 | ||
15 | namespace boost { namespace parameter { | |
16 | ||
17 | // A metafunction that, given an argument pack, returns the type of | |
18 | // the parameter identified by the given keyword. If no such | |
19 | // parameter has been specified, returns Default | |
20 | ||
21 | # if BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564)) | |
22 | template <class Parameters, class Keyword, class Default> | |
23 | struct value_type0 | |
24 | { | |
25 | typedef typename mpl::apply_wrap3< | |
26 | typename Parameters::binding,Keyword,Default,mpl::false_ | |
27 | >::type type; | |
28 | ||
29 | BOOST_MPL_ASSERT_NOT(( | |
30 | mpl::and_< | |
31 | is_same<Default, void_> | |
32 | , is_same<type, void_> | |
33 | > | |
34 | )); | |
35 | }; | |
36 | # endif | |
37 | ||
38 | template <class Parameters, class Keyword, class Default = void_> | |
39 | struct value_type | |
40 | { | |
41 | # if BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564)) | |
42 | typedef typename mpl::eval_if< | |
43 | mpl::is_placeholder<Parameters> | |
44 | , mpl::identity<int> | |
45 | , value_type0<Parameters,Keyword,Default> | |
46 | >::type type; | |
47 | # else | |
48 | typedef typename mpl::apply_wrap3< | |
49 | typename Parameters::binding,Keyword,Default,mpl::false_ | |
50 | >::type type; | |
51 | ||
52 | BOOST_MPL_ASSERT_NOT(( | |
53 | mpl::and_< | |
54 | is_same<Default, void_> | |
55 | , is_same<type, void_> | |
56 | > | |
57 | )); | |
58 | # endif | |
59 | ||
60 | BOOST_MPL_AUX_LAMBDA_SUPPORT(3,value_type,(Parameters,Keyword,Default)) | |
61 | }; | |
62 | ||
63 | // A metafunction that, given an argument pack, returns the type of | |
64 | // the parameter identified by the given keyword. If no such | |
65 | // parameter has been specified, returns the type returned by invoking | |
66 | // DefaultFn | |
67 | template <class Parameters, class Keyword, class DefaultFn> | |
68 | struct lazy_value_type | |
69 | { | |
70 | typedef typename mpl::apply_wrap3< | |
71 | typename Parameters::binding | |
72 | , Keyword | |
73 | , typename aux::result_of0<DefaultFn>::type | |
74 | , mpl::false_ | |
75 | >::type type; | |
76 | }; | |
77 | ||
78 | ||
79 | }} // namespace boost::parameter | |
80 | ||
81 | #endif // BOOST_PARAMETER_VALUE_TYPE_060921_HPP | |
82 |