469 lines
14 KiB
C++
469 lines
14 KiB
C++
/*=============================================================================
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Copyright (c) 2014 Paul Fultz II
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placeholders.h
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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==============================================================================*/
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#ifndef BOOST_HOF_GUARD_FUNCTION_PLACEHOLDERS_H
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#define BOOST_HOF_GUARD_FUNCTION_PLACEHOLDERS_H
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/// placeholders
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/// ============
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///
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/// Description
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/// -----------
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///
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/// The placeholders provide `std::bind` compatible placeholders that
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/// additionally provide basic C++ operators that creates bind expressions.
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/// Each bind expression supports `constexpr` function evaluation.
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///
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/// Synopsis
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/// --------
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///
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/// namespace placeholders {
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/// placeholder<1> _1 = {};
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/// placeholder<2> _2 = {};
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/// placeholder<3> _3 = {};
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/// placeholder<4> _4 = {};
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/// placeholder<5> _5 = {};
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/// placeholder<6> _6 = {};
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/// placeholder<7> _7 = {};
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/// placeholder<8> _8 = {};
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/// placeholder<9> _9 = {};
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/// }
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///
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/// Operators
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/// ---------
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///
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/// * Binary operators: +,-,*,/,%,>>,<<,>,<,<=,>=,==,!=,&,^,|,&&,||
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/// * Assign operators: +=,-=,*=,/=,%=,>>=,<<=,&=,|=,^=
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/// * Unary operators: !,~,+,-,*,++,--
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///
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///
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/// Example
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/// -------
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///
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/// #include <boost/hof.hpp>
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/// #include <cassert>
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/// using namespace boost::hof;
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///
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/// int main() {
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/// auto sum = _1 + _2;
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/// assert(3 == sum(1, 2));
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/// }
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///
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///
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/// unamed placeholder
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/// ==================
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///
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/// Description
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/// -----------
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///
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/// The unamed placeholder can be used to build simple functions from C++
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/// operators.
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///
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/// Note: The function produced by the unamed placeholder is not a bind expression.
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///
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/// Synopsis
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/// --------
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///
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/// namespace placeholders {
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/// /* unspecified */ _ = {};
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/// }
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///
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/// Example
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/// -------
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///
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/// #include <boost/hof.hpp>
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/// #include <cassert>
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/// using namespace boost::hof;
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///
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/// int main() {
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/// auto sum = _ + _;
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/// assert(3 == sum(1, 2));
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/// }
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///
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#include <boost/hof/returns.hpp>
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#include <boost/hof/lazy.hpp>
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#include <boost/hof/protect.hpp>
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#if defined(_MSC_VER) && _MSC_VER >= 1910
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#include <boost/hof/detail/pp.hpp>
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#endif
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namespace boost { namespace hof { namespace detail {
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template<int N>
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struct simple_placeholder
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{};
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}}} // namespace boost::hof
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namespace std {
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template<int N>
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struct is_placeholder<boost::hof::detail::simple_placeholder<N>>
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: std::integral_constant<int, N>
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{};
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}
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namespace boost { namespace hof {
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#define BOOST_HOF_FOREACH_BINARY_OP(m) \
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m(+, add) \
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m(-, subtract) \
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m(*, multiply) \
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m(/, divide) \
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m(%, remainder) \
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m(>>, shift_right) \
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m(<<, shift_left) \
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m(>, greater_than) \
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m(<, less_than) \
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m(<=, less_than_equal) \
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m(>=, greater_than_equal) \
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m(==, equal) \
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m(!=, not_equal) \
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m(&, bit_and) \
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m(^, xor_) \
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m(|, bit_or) \
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m(&&, and_) \
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m(||, or_)
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#define BOOST_HOF_FOREACH_ASSIGN_OP(m) \
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m(+=, assign_add) \
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m(-=, assign_subtract) \
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m(*=, assign_multiply) \
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m(/=, assign_divide) \
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m(%=, assign_remainder) \
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m(>>=, assign_right_shift) \
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m(<<=, assign_left_shift) \
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m(&=, assign_bit_and) \
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m(|=, assign_bit_or) \
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m(^=, assign_xor)
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#ifndef _MSC_VER
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#define BOOST_HOF_FOREACH_UNARY_OP(m) \
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m(!, not_) \
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m(~, compl_) \
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m(+, unary_plus) \
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m(-, unary_subtract) \
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m(*, dereference) \
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m(++, increment) \
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m(--, decrement)
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#else
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#define BOOST_HOF_FOREACH_UNARY_OP(m) \
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m(!, not_) \
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m(~, compl_) \
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m(+, unary_plus) \
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m(-, unary_subtract) \
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m(*, dereference)
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#endif
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namespace operators {
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struct call
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{
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template<class F, class... Ts>
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constexpr auto operator()(F&& f, Ts&&... xs) const BOOST_HOF_RETURNS
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(f(BOOST_HOF_FORWARD(Ts)(xs)...));
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};
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// MSVC 2017 ICEs on && and || in conxtexpr, so we fallback on bitwise operators
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#if defined(_MSC_VER) && _MSC_VER >= 1910
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#define BOOST_HOF_BINARY_OP_SKIP_and_ ()
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#define BOOST_HOF_BINARY_OP_SKIP_or_ ()
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struct and_
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{
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template<class T, class U>
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constexpr auto operator()(T&& x, U&& y) const
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noexcept(noexcept(BOOST_HOF_FORWARD(T)(x) && BOOST_HOF_FORWARD(U)(y)))
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-> decltype(BOOST_HOF_FORWARD(T)(x) && BOOST_HOF_FORWARD(U)(y))
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{ return BOOST_HOF_FORWARD(T)(x) & BOOST_HOF_FORWARD(U)(y); }
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};
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struct or_
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{
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template<class T, class U>
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constexpr auto operator()(T&& x, U&& y) const
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noexcept(noexcept(BOOST_HOF_FORWARD(T)(x) || BOOST_HOF_FORWARD(U)(y)))
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-> decltype(BOOST_HOF_FORWARD(T)(x) || BOOST_HOF_FORWARD(U)(y))
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{ return BOOST_HOF_FORWARD(T)(x) | BOOST_HOF_FORWARD(U)(y); }
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};
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#define BOOST_HOF_BINARY_OP_IMPL(op, name) \
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struct name \
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{ \
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template<class T, class U> \
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BOOST_HOF_USING(ex_failure, decltype(std::declval<T>() op std::declval<U>())); \
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struct failure : as_failure<ex_failure> {}; \
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template<class T, class U> \
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constexpr auto operator()(T&& x, U&& y) const BOOST_HOF_RETURNS \
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(BOOST_HOF_FORWARD(T)(x) op BOOST_HOF_FORWARD(U)(y)); \
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};
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#define BOOST_HOF_BINARY_OP(op, name) \
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BOOST_HOF_PP_IIF(BOOST_HOF_PP_IS_PAREN(BOOST_HOF_PP_CAT(BOOST_HOF_BINARY_OP_SKIP_, name))) \
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(BOOST_HOF_PP_EMPTY, BOOST_HOF_BINARY_OP_IMPL)(op, name)
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#else
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#define BOOST_HOF_BINARY_OP(op, name) \
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struct name \
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{ \
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template<class T, class U> \
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constexpr auto operator()(T&& x, U&& y) const BOOST_HOF_RETURNS \
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(BOOST_HOF_FORWARD(T)(x) op BOOST_HOF_FORWARD(U)(y)); \
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};
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#endif
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BOOST_HOF_FOREACH_BINARY_OP(BOOST_HOF_BINARY_OP)
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BOOST_HOF_FOREACH_ASSIGN_OP(BOOST_HOF_BINARY_OP)
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#define BOOST_HOF_UNARY_OP(op, name) \
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struct name \
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{ \
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template<class T> \
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constexpr auto operator()(T&& x) const BOOST_HOF_RETURNS \
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(op(BOOST_HOF_FORWARD(T)(x))); \
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};
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BOOST_HOF_FOREACH_UNARY_OP(BOOST_HOF_UNARY_OP)
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}
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template<int N>
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struct placeholder
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{
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#if BOOST_HOF_HAS_MANGLE_OVERLOAD
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template<class... Ts>
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constexpr auto operator()(Ts&&... xs) const BOOST_HOF_RETURNS
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( boost::hof::lazy(operators::call())(detail::simple_placeholder<N>(), BOOST_HOF_FORWARD(Ts)(xs)...) );
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#else
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template<class... Ts>
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struct result_call
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{ typedef decltype(boost::hof::lazy(operators::call())(detail::simple_placeholder<N>(), std::declval<Ts>()...)) type; };
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template<class... Ts>
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constexpr typename result_call<Ts...>::type operator()(Ts&&... xs) const
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{ return boost::hof::lazy(operators::call())(detail::simple_placeholder<N>(), BOOST_HOF_FORWARD(Ts)(xs)...); };
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#endif
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#define BOOST_HOF_PLACEHOLDER_UNARY_OP(op, name) \
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constexpr auto operator op () const BOOST_HOF_RETURNS \
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( boost::hof::lazy(operators::name())(detail::simple_placeholder<N>()) );
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BOOST_HOF_FOREACH_UNARY_OP(BOOST_HOF_PLACEHOLDER_UNARY_OP)
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#define BOOST_HOF_PLACEHOLDER_ASSIGN_OP(op, name) \
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template<class T> \
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constexpr auto operator op (T&& x) const BOOST_HOF_RETURNS \
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( boost::hof::lazy(operators::name())(detail::simple_placeholder<N>(), BOOST_HOF_FORWARD(T)(x)) );
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BOOST_HOF_FOREACH_ASSIGN_OP(BOOST_HOF_PLACEHOLDER_ASSIGN_OP)
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};
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#if BOOST_HOF_HAS_MANGLE_OVERLOAD
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#define BOOST_HOF_PLACEHOLDER_BINARY_OP(op, name) \
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template<class T, int N> \
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constexpr inline auto operator op (const placeholder<N>&, T&& x) BOOST_HOF_RETURNS \
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( boost::hof::lazy(operators::name())(detail::simple_placeholder<N>(), BOOST_HOF_FORWARD(T)(x)) ); \
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template<class T, int N> \
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constexpr inline auto operator op (T&& x, const placeholder<N>&) BOOST_HOF_RETURNS \
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( boost::hof::lazy(operators::name())(BOOST_HOF_FORWARD(T)(x), detail::simple_placeholder<N>()) ); \
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template<int N, int M> \
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constexpr inline auto operator op (const placeholder<N>&, const placeholder<M>&) BOOST_HOF_RETURNS \
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( boost::hof::lazy(operators::name())(detail::simple_placeholder<N>(), detail::simple_placeholder<M>()) );
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#else
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#define BOOST_HOF_PLACEHOLDER_BINARY_OP(op, name) \
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template<class T, class U> \
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struct result_ ## name \
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{ typedef decltype(boost::hof::lazy(operators::name())(std::declval<T>(), std::declval<U>())) type; }; \
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template<class T, int N> \
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constexpr inline typename result_ ## name<detail::simple_placeholder<N>, T>::type operator op (const placeholder<N>&, T&& x) \
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{ return boost::hof::lazy(operators::name())(detail::simple_placeholder<N>(), BOOST_HOF_FORWARD(T)(x)); } \
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template<class T, int N> \
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constexpr inline typename result_ ## name<T, detail::simple_placeholder<N>>::type operator op (T&& x, const placeholder<N>&) \
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{ return boost::hof::lazy(operators::name())(BOOST_HOF_FORWARD(T)(x), detail::simple_placeholder<N>()); } \
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template<int N, int M> \
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constexpr inline typename result_ ## name<detail::simple_placeholder<N>, detail::simple_placeholder<M>>::type operator op (const placeholder<N>&, const placeholder<M>&) \
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{ return boost::hof::lazy(operators::name())(detail::simple_placeholder<N>(), detail::simple_placeholder<M>()); }
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#endif
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BOOST_HOF_FOREACH_BINARY_OP(BOOST_HOF_PLACEHOLDER_BINARY_OP)
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namespace placeholders {
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BOOST_HOF_DECLARE_STATIC_VAR(_1, placeholder<1>);
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BOOST_HOF_DECLARE_STATIC_VAR(_2, placeholder<2>);
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BOOST_HOF_DECLARE_STATIC_VAR(_3, placeholder<3>);
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BOOST_HOF_DECLARE_STATIC_VAR(_4, placeholder<4>);
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BOOST_HOF_DECLARE_STATIC_VAR(_5, placeholder<5>);
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BOOST_HOF_DECLARE_STATIC_VAR(_6, placeholder<6>);
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BOOST_HOF_DECLARE_STATIC_VAR(_7, placeholder<7>);
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BOOST_HOF_DECLARE_STATIC_VAR(_8, placeholder<8>);
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BOOST_HOF_DECLARE_STATIC_VAR(_9, placeholder<9>);
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}
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using placeholders::_1;
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using placeholders::_2;
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using placeholders::_3;
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using placeholders::_4;
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using placeholders::_5;
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using placeholders::_6;
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using placeholders::_7;
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using placeholders::_8;
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using placeholders::_9;
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namespace detail {
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struct unamed_placeholder
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{
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template<class T, class Invoker>
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struct partial_ap
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{
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T val;
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BOOST_HOF_INHERIT_DEFAULT_EMPTY(partial_ap, T)
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template<class X, class... Xs, BOOST_HOF_ENABLE_IF_CONSTRUCTIBLE(T, X&&, Xs&&...)>
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constexpr partial_ap(X&& x, Xs&&... xs) : val(BOOST_HOF_FORWARD(X)(x), BOOST_HOF_FORWARD(Xs)(xs)...)
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{}
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BOOST_HOF_RETURNS_CLASS(partial_ap);
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struct partial_ap_failure
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{
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template<class Failure>
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struct apply
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{
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template<class... Xs>
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struct of;
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template<class X>
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struct of<X>
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: Failure::template of<typename std::add_const<T>::type, X>
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{};
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};
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};
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struct failure
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: failure_map<partial_ap_failure, Invoker>
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{};
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template<class X>
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constexpr BOOST_HOF_SFINAE_RESULT(const Invoker&, id_<T>, id_<X>)
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operator()(X&& x) const BOOST_HOF_SFINAE_RETURNS
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(
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Invoker()(BOOST_HOF_CONST_THIS->val, BOOST_HOF_FORWARD(X)(x))
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);
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};
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template<class Invoker, class T>
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static constexpr partial_ap<T, Invoker> make_partial_ap(T&& x)
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{
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return {BOOST_HOF_FORWARD(T)(x)};
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}
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template<class Op>
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struct left
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{
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struct failure
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: failure_for<Op>
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{};
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template<class T, class X>
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constexpr BOOST_HOF_SFINAE_RESULT(const Op&, id_<T>, id_<X>)
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operator()(T&& val, X&& x) const BOOST_HOF_SFINAE_RETURNS
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(Op()(BOOST_HOF_FORWARD(T)(val), BOOST_HOF_FORWARD(X)(x)));
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};
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template<class Op>
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struct right
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{
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struct right_failure
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{
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template<class Failure>
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struct apply
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{
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template<class T, class U, class... Ts>
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struct of
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: Failure::template of<U, T, Ts...>
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{};
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};
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};
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struct failure
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: failure_map<right_failure, Op>
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{};
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template<class T, class X>
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constexpr BOOST_HOF_SFINAE_RESULT(const Op&, id_<X>, id_<T>)
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operator()(T&& val, X&& x) const BOOST_HOF_SFINAE_RETURNS
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(Op()(BOOST_HOF_FORWARD(X)(x), BOOST_HOF_FORWARD(T)(val)));
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};
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#define BOOST_HOF_UNAMED_PLACEHOLDER_UNARY_OP(op, name) \
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constexpr auto operator op () const BOOST_HOF_RETURNS \
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( operators::name() );
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BOOST_HOF_FOREACH_UNARY_OP(BOOST_HOF_UNAMED_PLACEHOLDER_UNARY_OP)
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#define BOOST_HOF_UNAMED_PLACEHOLDER_ASSIGN_OP(op, name) \
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template<class T> \
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constexpr auto operator op (const T& x) const BOOST_HOF_RETURNS \
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( partial_ap<T, left<operators::name>>(x) );
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BOOST_HOF_FOREACH_ASSIGN_OP(BOOST_HOF_UNAMED_PLACEHOLDER_ASSIGN_OP)
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};
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#define BOOST_HOF_UNAMED_PLACEHOLDER_BINARY_OP(op, name) \
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template<class T> \
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constexpr inline auto operator op (const unamed_placeholder&, const T& x) BOOST_HOF_RETURNS \
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( unamed_placeholder::make_partial_ap<unamed_placeholder::right<operators::name>>(boost::hof::decay(x)) ); \
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template<class T> \
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constexpr inline auto operator op (const T& x, const unamed_placeholder&) BOOST_HOF_RETURNS \
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( unamed_placeholder::make_partial_ap<unamed_placeholder::left<operators::name>>(boost::hof::decay(x)) ); \
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constexpr inline auto operator op (const unamed_placeholder&, const unamed_placeholder&) BOOST_HOF_RETURNS \
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( operators::name() );
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BOOST_HOF_FOREACH_BINARY_OP(BOOST_HOF_UNAMED_PLACEHOLDER_BINARY_OP)
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}
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namespace placeholders {
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BOOST_HOF_DECLARE_STATIC_VAR(_, detail::unamed_placeholder);
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}
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using placeholders::_;
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}} // namespace boost::hof
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namespace std {
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template<int N>
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struct is_placeholder<boost::hof::placeholder<N>>
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: std::integral_constant<int, N>
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{};
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}
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namespace boost {
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template<class T>
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struct is_placeholder;
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template<int N>
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struct is_placeholder<boost::hof::placeholder<N>>
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: std::integral_constant<int, N>
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{};
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}
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#endif
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