source: NonGTP/Boost/boost/parameter/aux_/default.hpp @ 857

Revision 857, 1.8 KB checked in by igarcia, 19 years ago (diff)
Line 
1// Copyright Daniel Wallin, David Abrahams 2005. Use, modification and
2// distribution is subject to the Boost Software License, Version 1.0. (See
3// accompanying file LICENSE_1_0.txt or copy at
4// http://www.boost.org/LICENSE_1_0.txt)
5
6#ifndef DEFAULT_050329_HPP
7#define DEFAULT_050329_HPP
8
9namespace boost { namespace parameter { namespace aux {
10
11// A wrapper for the default value passed by the user when resolving
12// the value of the parameter with the given Keyword
13template <class Keyword, class Value>
14struct default_
15{
16    default_(Value& x)
17      : value(x)
18    {}
19
20    Value& value;
21};
22
23//
24// lazy_default --
25//
26//    A wrapper for the default value computation function passed by
27//    the user when resolving the value of the parameter with the
28//    given keyword
29//
30#if BOOST_WORKAROUND(__EDG_VERSION__, <= 300)
31// These compilers need a little extra help with overload
32// resolution; we have empty_arg_list's operator[] accept a base
33// class to make that overload less preferable.
34template <class KW, class DefaultComputer>
35struct lazy_default_base
36{
37    lazy_default_base(DefaultComputer const& x)
38      : compute_default(x)
39    {}
40    DefaultComputer const& compute_default;
41};
42
43template <class KW, class DefaultComputer>
44struct lazy_default
45  : lazy_default_base<KW,DefaultComputer>
46  {
47      lazy_default(DefaultComputer const & x)
48        : lazy_default_base<KW,DefaultComputer>(x)
49      {}
50  };
51# define BOOST_PARAMETER_lazy_default_fallback lazy_default_base
52#else
53template <class KW, class DefaultComputer>
54struct lazy_default
55{
56    lazy_default(const DefaultComputer& x)
57      : compute_default(x)
58    {}
59    DefaultComputer const& compute_default;
60};
61# define BOOST_PARAMETER_lazy_default_fallback lazy_default
62#endif
63
64}}} // namespace boost::parameter::aux
65
66#endif // DEFAULT_050329_HPP
67
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