forked from boostorg/range
Jean-Philippe DUFRAIGNE
1b4f8100ef
Lambda has no default constructor nor a copy or move assignment. range\test\adaptors.cpp is checking that produced ranges are copiable, but it is not doing so the for lambda, or lambda like objects. default_constructible_unary_fn uses an optional for default construction. I extended it to use its emplace facility to copy assign non copy assignable types. (see boost::optional 'Type Requierment': 'If T is not MoveAssignable, it is still possible to reset the value of optional<T> using function emplace():')
82 lines
2.0 KiB
C++
82 lines
2.0 KiB
C++
// Boost.Range library
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//
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// Copyright Neil Groves 2014. Use, modification and
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// distribution is subject to the Boost Software License, Version
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// 1.0. (See 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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//
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// For more information, see http://www.boost.org/libs/range/
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//
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#ifndef BOOST_RANGE_DETAIL_DEFAULT_CONSTRUCTIBLE_UNARY_FN_HPP_INCLUDED
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#define BOOST_RANGE_DETAIL_DEFAULT_CONSTRUCTIBLE_UNARY_FN_HPP_INCLUDED
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#include <boost/optional/optional.hpp>
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#include <boost/mpl/if.hpp>
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#include <boost/type_traits/has_trivial_constructor.hpp>
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namespace boost
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{
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namespace range_detail
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{
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template<typename F, typename R>
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class default_constructible_unary_fn_wrapper
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{
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public:
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typedef R result_type;
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default_constructible_unary_fn_wrapper()
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{
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}
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default_constructible_unary_fn_wrapper(const F& source)
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: m_impl(source)
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{
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}
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default_constructible_unary_fn_wrapper(const default_constructible_unary_fn_wrapper& source)
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: m_impl(source.m_impl)
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{
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}
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default_constructible_unary_fn_wrapper& operator=(const default_constructible_unary_fn_wrapper& source)
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{
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if (source.m_impl)
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{
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// Lambda are not copy/move assignable.
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m_impl.emplace(*source.m_impl);
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}
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else
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{
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m_impl.reset();
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}
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return *this;
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}
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template<typename Arg>
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R operator()(const Arg& arg) const
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{
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BOOST_ASSERT(m_impl);
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return (*m_impl)(arg);
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}
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template<typename Arg>
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R operator()(Arg& arg) const
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{
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BOOST_ASSERT(m_impl);
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return (*m_impl)(arg);
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}
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private:
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boost::optional<F> m_impl;
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};
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template<typename F, typename R>
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struct default_constructible_unary_fn_gen
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{
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typedef typename boost::mpl::if_<
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boost::has_trivial_default_constructor<F>,
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F,
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default_constructible_unary_fn_wrapper<F,R>
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>::type type;
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};
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} // namespace range_detail
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} // namespace boost
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#endif // include guard
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