123 lines
4.0 KiB
C++
123 lines
4.0 KiB
C++
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// 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 KEYWORD_050328_HPP
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#define KEYWORD_050328_HPP
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#include <boost/parameter/aux_/unwrap_cv_reference.hpp>
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#include <boost/parameter/aux_/tag.hpp>
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#include <boost/parameter/aux_/default.hpp>
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namespace boost { namespace parameter {
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// Instances of unique specializations of keyword<...> serve to
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// associate arguments with parameter names. For example:
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//
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// struct rate_; // parameter names
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// struct skew_;
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// namespace
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// {
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// keyword<rate_> rate; // keywords
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// keyword<skew_> skew;
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// }
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//
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// ...
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//
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// f(rate = 1, skew = 2.4);
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//
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template <class Tag>
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struct keyword
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{
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template <class T>
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typename aux::tag<Tag, T>::type const
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operator=(T& x) const
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{
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typedef typename aux::tag<Tag, T>::type result;
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return result(x);
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}
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template <class Default>
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aux::default_<Tag, Default>
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operator|(Default& default_) const
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{
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return aux::default_<Tag, Default>(default_);
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}
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template <class Default>
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aux::lazy_default<Tag, Default>
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operator||(Default& default_) const
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{
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return aux::lazy_default<Tag, Default>(default_);
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}
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template <class T>
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typename aux::tag<Tag, T const>::type const
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operator=(T const& x) const
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{
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typedef typename aux::tag<Tag, T const>::type result;
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return result(x);
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}
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template <class Default>
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aux::default_<Tag, const Default>
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operator|(const Default& default_) const
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{
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return aux::default_<Tag, const Default>(default_);
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}
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template <class Default>
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aux::lazy_default<Tag, Default>
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operator||(Default const& default_) const
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{
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return aux::lazy_default<Tag, Default>(default_);
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}
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public: // Insurance against ODR violations
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// People will need to define these keywords in header files. To
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// prevent ODR violations, it's important that the keyword used in
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// every instantiation of a function template is the same object.
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// We provide a reference to a common instance of each keyword
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// object and prevent construction by users.
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static keyword<Tag> const instance;
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// This interface is deprecated
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static keyword<Tag>& get()
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{
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return const_cast<keyword<Tag>&>(instance);
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}
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};
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template <class Tag>
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keyword<Tag> const keyword<Tag>::instance = {};
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// Reduces boilerplate required to declare and initialize keywords
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// without violating ODR. Declares a keyword tag type with the given
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// name in namespace tag_namespace, and declares and initializes a
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// reference in an anonymous namespace to a singleton instance of that
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// type.
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#define BOOST_PARAMETER_KEYWORD(tag_namespace,name) \
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namespace tag_namespace \
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{ \
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struct name \
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{ \
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static char const* keyword_name() \
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{ \
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return #name; \
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} \
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}; \
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} \
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namespace \
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{ \
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::boost::parameter::keyword<tag_namespace::name> const& name \
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= ::boost::parameter::keyword<tag_namespace::name>::instance;\
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}
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}} // namespace boost::parameter
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#endif // KEYWORD_050328_HPP
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