append.hpp
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/*!
@file
Forward declares `boost::hana::append`.
Copyright Louis Dionne 2013-2022
Distributed under the Boost Software License, Version 1.0.
(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
*/
#ifndef BOOST_HANA_FWD_APPEND_HPP
#define BOOST_HANA_FWD_APPEND_HPP
#include <boost/hana/config.hpp>
#include <boost/hana/core/when.hpp>
namespace boost { namespace hana {
//! Append an element to a monadic structure.
//! @ingroup group-MonadPlus
//!
//! Given an element `x` and a monadic structure `xs`, `append` returns a
//! new monadic structure which is the result of lifting `x` into the
//! monadic structure and then combining that (to the right) with `xs`.
//! In other words,
//! @code
//! append(xs, x) == concat(xs, lift<Xs>(x))
//! @endcode
//! where `Xs` is the tag of `xs`. For sequences, this has the intuitive
//! behavior of simply appending an element to the end of the sequence,
//! hence the name.
//!
//! > #### Rationale for not calling this `push_back`
//! > See the rationale for using `prepend` instead of `push_front`.
//!
//!
//! Signature
//! ---------
//! Given a MonadPlus `M`, the signature is
//! @f$ \mathtt{append} : M(T) \times T \to M(T) @f$.
//!
//! @param xs
//! A monadic structure that will be combined to the left of the element.
//!
//! @param x
//! An element to combine to the right of the monadic structure.
//!
//!
//! Example
//! -------
//! @include example/append.cpp
#ifdef BOOST_HANA_DOXYGEN_INVOKED
constexpr auto append = [](auto&& xs, auto&& x) {
return tag-dispatched;
};
#else
template <typename M, typename = void>
struct append_impl : append_impl<M, when<true>> { };
struct append_t {
template <typename Xs, typename X>
constexpr auto operator()(Xs&& xs, X&& x) const;
};
BOOST_HANA_INLINE_VARIABLE constexpr append_t append{};
#endif
}} // end namespace boost::hana
#endif // !BOOST_HANA_FWD_APPEND_HPP