hana/fwd/repeat.hpp

0001 /*!
0002 @file
0003 Forward declares `boost::hana::repeat`.
0004
0005 Copyright Louis Dionne 2013-2022
0006 Distributed under the Boost Software License, Version 1.0.
0007 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
0008  */
0009
0010 #ifndef BOOST_HANA_FWD_REPEAT_HPP
0011 #define BOOST_HANA_FWD_REPEAT_HPP
0012
0013 #include <boost/hana/config.hpp>
0014 #include <boost/hana/core/when.hpp>
0015
0016
0017 namespace boost { namespace hana {
0018     //! Invokes a nullary function `n` times.
0019     //! @ingroup group-IntegralConstant
0020     //!
0021     //! Given an `IntegralConstant` `n` and a nullary function `f`,
0022     //! `repeat(n, f)` will call `f` `n` times. In particular, any
0023     //! decent compiler should expand `repeat(n, f)` to
0024     //! @code
0025     //!     f(); f(); ... f(); // n times total
0026     //! @endcode
0027     //!
0028     //!
0029     //! @param n
0030     //! An `IntegralConstant` holding a non-negative value representing
0031     //! the number of times `f` should be repeatedly invoked.
0032     //!
0033     //! @param f
0034     //! A function to repeatedly invoke `n` times. `f` is allowed to have
0035     //! side effects.
0036     //!
0037     //!
0038     //! Example
0039     //! -------
0040     //! @include example/repeat.cpp
0041 #ifdef BOOST_HANA_DOXYGEN_INVOKED
0042     constexpr auto repeat = [](auto const& n, auto&& f) -> void {
0043         f(); f(); ... f(); // n times total
0044     };
0045 #else
0046     template <typename N, typename = void>
0047     struct repeat_impl : repeat_impl<N, when<true>> { };
0048
0049     struct repeat_t {
0050         template <typename N, typename F>
0051         constexpr void operator()(N const& n, F&& f) const;
0052     };
0053
0054     BOOST_HANA_INLINE_VARIABLE constexpr repeat_t repeat{};
0055 #endif
0056 }} // end namespace boost::hana
0057
0058 #endif // !BOOST_HANA_FWD_REPEAT_HPP