70 lines
1.9 KiB
C++
70 lines
1.9 KiB
C++
// Copyright Daniel Wallin, David Abrahams 2005. Use, modification and
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// distribution is subject to the Boost Software License, Version 1.0. (See
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// accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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#ifndef DEFAULT_050329_HPP
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# define DEFAULT_050329_HPP
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# include <boost/detail/workaround.hpp>
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namespace boost { namespace parameter { namespace aux {
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// A wrapper for the default value passed by the user when resolving
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// the value of the parameter with the given Keyword
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template <class Keyword, class Value>
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struct default_
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{
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default_(Value& x)
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: value(x)
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{}
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Value& value;
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};
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//
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// lazy_default --
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//
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// A wrapper for the default value computation function passed by
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// the user when resolving the value of the parameter with the
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// given keyword
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//
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# if BOOST_WORKAROUND(__EDG_VERSION__, <= 300)
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// These compilers need a little extra help with overload
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// resolution; we have empty_arg_list's operator[] accept a base
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// class to make that overload less preferable.
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template <class KW, class DefaultComputer>
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struct lazy_default_base
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{
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lazy_default_base(DefaultComputer const& x)
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: compute_default(x)
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{}
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DefaultComputer const& compute_default;
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};
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template <class KW, class DefaultComputer>
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struct lazy_default
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: lazy_default_base<KW,DefaultComputer>
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{
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lazy_default(DefaultComputer const & x)
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: lazy_default_base<KW,DefaultComputer>(x)
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{}
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};
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# define BOOST_PARAMETER_lazy_default_fallback lazy_default_base
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# else
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template <class KW, class DefaultComputer>
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struct lazy_default
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{
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lazy_default(const DefaultComputer& x)
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: compute_default(x)
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{}
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DefaultComputer const& compute_default;
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};
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# define BOOST_PARAMETER_lazy_default_fallback lazy_default
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# endif
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}}} // namespace boost::parameter::aux
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#endif // DEFAULT_050329_HPP
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