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70 lines
2.2 KiB
C++
70 lines
2.2 KiB
C++
/*!
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@file
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Forward declares `boost::hana::remove_if`.
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@copyright Louis Dionne 2013-2016
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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*/
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#ifndef BOOST_HANA_FWD_REMOVE_IF_HPP
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#define BOOST_HANA_FWD_REMOVE_IF_HPP
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#include <boost/hana/config.hpp>
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#include <boost/hana/core/when.hpp>
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BOOST_HANA_NAMESPACE_BEGIN
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//! Remove all the elements of a monadic structure that satisfy some
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//! predicate.
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//! @ingroup group-MonadPlus
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//!
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//! Given a monadic structure `xs` and a unary predicate, `remove_if`
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//! returns a new monadic structure equal to `xs` without all its elements
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//! that satisfy the predicate. This is equivalent to `filter` with a
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//! negated predicate, i.e.
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//! @code
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//! remove_if(xs, predicate) == filter(xs, negated predicated)
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//! @endcode
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//!
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//!
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//! Signature
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//! ---------
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//! Given a MonadPlus `M` and a predicate of type \f$ T \to Bool \f$ for
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//! some compile-time Logical `Bool`, the signature is
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//! \f$
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//! \mathrm{remove\_if} : M(T) \times (T \to Bool) \to M(T)
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//! \f$
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//!
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//! @param xs
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//! A monadic structure to remove some elements from.
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//!
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//! @param predicate
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//! A unary predicate called as `predicate(x)`, where `x` is an element
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//! of the structure, and returning whether `x` should be removed from
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//! the structure. In the current version of the library, `predicate`
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//! must return a compile-time Logical.
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//!
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//!
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//! Example
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//! -------
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//! @include example/remove_if.cpp
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#ifdef BOOST_HANA_DOXYGEN_INVOKED
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constexpr auto remove_if = [](auto&& xs, auto&& predicate) {
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return tag-dispatched;
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};
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#else
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template <typename M, typename = void>
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struct remove_if_impl : remove_if_impl<M, when<true>> { };
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struct remove_if_t {
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template <typename Xs, typename Pred>
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constexpr auto operator()(Xs&& xs, Pred&& pred) const;
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};
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constexpr remove_if_t remove_if{};
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#endif
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_FWD_REMOVE_IF_HPP
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