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 

     9 namespace 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

    13 template <class Keyword, class Value>

    14 struct 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.

    34 template <class KW, class DefaultComputer>

    35 struct lazy_default_base

    36 {

    37     lazy_default_base(DefaultComputer const& x)

    38       : compute_default(x)

    39     {}

    40     DefaultComputer const& compute_default;

    41 };

    42 

    43 template <class KW, class DefaultComputer>

    44 struct 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 

    53 template <class KW, class DefaultComputer>

    54 struct 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