mirror of
https://github.com/ecency/ecency-mobile.git
synced 2024-12-26 23:05:00 +03:00
104 lines
3.9 KiB
C++
104 lines
3.9 KiB
C++
/*!
|
|
@file
|
|
Forward declares `boost::hana::group`.
|
|
|
|
@copyright Louis Dionne 2013-2016
|
|
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_GROUP_HPP
|
|
#define BOOST_HANA_FWD_GROUP_HPP
|
|
|
|
#include <boost/hana/config.hpp>
|
|
#include <boost/hana/core/when.hpp>
|
|
#include <boost/hana/detail/nested_by_fwd.hpp>
|
|
|
|
|
|
BOOST_HANA_NAMESPACE_BEGIN
|
|
//! Group adjacent elements of a sequence that all respect a binary
|
|
//! predicate, by default equality.
|
|
//! @ingroup group-Sequence
|
|
//!
|
|
//! Given a _finite_ Sequence and an optional predicate (by default
|
|
//! `equal`), `group` returns a sequence of subsequences representing
|
|
//! groups of adjacent elements that are "equal" with respect to the
|
|
//! predicate. In other words, the groups are such that the predicate is
|
|
//! satisfied when it is applied to any two adjacent elements in that
|
|
//! group. The sequence returned by `group` is such that the concatenation
|
|
//! of its elements is equal to the original sequence, which is equivalent
|
|
//! to saying that the order of the elements is not changed.
|
|
//!
|
|
//! If no predicate is provided, adjacent elements in the sequence must
|
|
//! all be compile-time `Comparable`.
|
|
//!
|
|
//!
|
|
//! Signature
|
|
//! ---------
|
|
//! Given a Sequence `s` with tag `S(T)`, an `IntegralConstant` `Bool`
|
|
//! holding a value of type `bool`, and a predicate
|
|
//! \f$ pred : T \times T \to Bool \f$, `group` has the following
|
|
//! signatures. For the variant with a provided predicate,
|
|
//! \f[
|
|
//! \mathtt{group} : S(T) \times (T \times T \to Bool) \to S(S(T))
|
|
//! \f]
|
|
//!
|
|
//! for the variant without a custom predicate, `T` is required to be
|
|
//! Comparable. The signature is then
|
|
//! \f[
|
|
//! \mathtt{group} : S(T) \to S(S(T))
|
|
//! \f]
|
|
//!
|
|
//! @param xs
|
|
//! The sequence to split into groups.
|
|
//!
|
|
//! @param predicate
|
|
//! A binary function called as `predicate(x, y)`, where `x` and `y` are
|
|
//! _adjacent_ elements in the sequence, whether both elements should be
|
|
//! in the same group (subsequence) of the result. In the current version
|
|
//! of the library, the result returned by `predicate` must be an
|
|
//! `IntegralConstant` holding a value of a type convertible to `bool`.
|
|
//! Also, `predicate` has to define an equivalence relation as defined by
|
|
//! the `Comparable` concept. When this predicate is not provided, it
|
|
//! defaults to `equal`, which requires the comparison of any two adjacent
|
|
//! elements in the sequence to return a boolean `IntegralConstant`.
|
|
//!
|
|
//!
|
|
//! Syntactic sugar (`group.by`)
|
|
//! ----------------------------
|
|
//! `group` can be called in a third way, which provides a nice syntax
|
|
//! especially when working with the `comparing` combinator:
|
|
//! @code
|
|
//! group.by(predicate, xs) == group(xs, predicate)
|
|
//! group.by(predicate) == group(-, predicate)
|
|
//! @endcode
|
|
//!
|
|
//! where `group(-, predicate)` denotes the partial application of
|
|
//! `group` to `predicate`.
|
|
//!
|
|
//!
|
|
//! Example
|
|
//! -------
|
|
//! @include example/group.cpp
|
|
#ifdef BOOST_HANA_DOXYGEN_INVOKED
|
|
constexpr auto group = [](auto&& xs[, auto&& predicate]) {
|
|
return tag-dispatched;
|
|
};
|
|
#else
|
|
template <typename S, typename = void>
|
|
struct group_impl : group_impl<S, when<true>> { };
|
|
|
|
struct group_t : detail::nested_by<group_t> {
|
|
template <typename Xs>
|
|
constexpr auto operator()(Xs&& xs) const;
|
|
|
|
template <typename Xs, typename Predicate>
|
|
constexpr auto operator()(Xs&& xs, Predicate&& pred) const;
|
|
};
|
|
|
|
constexpr group_t group{};
|
|
#endif
|
|
BOOST_HANA_NAMESPACE_END
|
|
|
|
#endif // !BOOST_HANA_FWD_GROUP_HPP
|