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+/*=============================================================================
+ Copyright (c) 2015 Paul Fultz II
+ decorate.h
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+==============================================================================*/
+
+#ifndef BOOST_HOF_GUARD_DECORATE_H
+#define BOOST_HOF_GUARD_DECORATE_H
+
+/// decorate
+/// ========
+///
+/// Description
+/// -----------
+///
+/// The `decorate` function adaptor helps create simple function decorators.
+///
+/// A function adaptor takes a function and returns a new functions whereas a
+/// decorator takes some parameters and returns a function adaptor. The
+/// `decorate` function adaptor will return a decorator that returns a
+/// function adaptor. Eventually, it will invoke the function with the user-
+/// provided parameter and function.
+///
+/// Synopsis
+/// --------
+///
+/// template<class F>
+/// constexpr decorate_adaptor<F> decorate(F f);
+///
+/// Semantics
+/// ---------
+///
+/// assert(decorate(f)(x)(g)(xs...) == f(x, g, xs...));
+///
+/// Requirements
+/// ------------
+///
+/// F must be:
+///
+/// * [ConstInvocable](ConstInvocable)
+/// * MoveConstructible
+///
+/// Example
+/// -------
+///
+/// #include <boost/hof.hpp>
+/// #include <cassert>
+/// #include <iostream>
+/// #include <string>
+/// using namespace boost::hof;
+///
+/// struct logger_f
+/// {
+/// template<class F, class... Ts>
+/// auto operator()(const std::string& message, F&& f, Ts&&... xs) const
+/// -> decltype(f(std::forward<Ts>(xs)...))
+/// {
+/// // Message to print out when the function is called
+/// std::cout << message << std::endl;
+/// // Call the function
+/// return f(std::forward<Ts>(xs)...);
+/// }
+/// };
+/// // The logger decorator
+/// BOOST_HOF_STATIC_FUNCTION(logger) = boost::hof::decorate(logger_f());
+///
+/// struct sum_f
+/// {
+/// template<class T, class U>
+/// T operator()(T x, U y) const
+/// {
+/// return x+y;
+/// }
+/// };
+///
+/// BOOST_HOF_STATIC_FUNCTION(sum) = sum_f();
+/// int main() {
+/// // Use the logger decorator to print "Calling sum" when the function is called
+/// assert(3 == logger("Calling sum")(sum)(1, 2));
+/// }
+///
+
+#include <boost/hof/reveal.hpp>
+#include <boost/hof/detail/delegate.hpp>
+#include <boost/hof/detail/move.hpp>
+#include <boost/hof/detail/make.hpp>
+#include <boost/hof/detail/callable_base.hpp>
+#include <boost/hof/detail/static_const_var.hpp>
+#include <boost/hof/detail/compressed_pair.hpp>
+
+namespace boost { namespace hof { namespace detail {
+
+template<class D, class T, class F>
+struct decorator_invoke
+// : compressed_pair<compressed_pair<F, T>, D>
+: compressed_pair<compressed_pair<D, T>, F>
+{
+ // typedef compressed_pair<F, T> base;
+ typedef compressed_pair<compressed_pair<D, T>, F> base;
+
+ BOOST_HOF_INHERIT_CONSTRUCTOR(decorator_invoke, base)
+
+ template<class... Ts>
+ constexpr const compressed_pair<D, T>& get_pair(Ts&&... xs) const noexcept
+ {
+ return this->first(xs...);
+ }
+
+ template<class... Ts>
+ constexpr const F& base_function(Ts&&... xs) const noexcept
+ {
+ return this->second(xs...);
+ }
+
+ template<class... Ts>
+ constexpr const D& get_decorator(Ts&&... xs) const noexcept
+ {
+ return this->get_pair(xs...).first(xs...);
+ }
+
+ template<class... Ts>
+ constexpr const T& get_data(Ts&&... xs) const noexcept
+ {
+ return this->get_pair(xs...).second(xs...);
+ }
+
+ BOOST_HOF_RETURNS_CLASS(decorator_invoke);
+
+ struct decorator_invoke_failure
+ {
+ template<class Failure>
+ struct apply
+ {
+ template<class... Ts>
+ struct of
+ : Failure::template of<const T&, const F&, Ts...>
+ {};
+ };
+ };
+
+ struct failure
+ : failure_map<decorator_invoke_failure, D>
+ {};
+
+ template<class... Ts>
+ constexpr BOOST_HOF_SFINAE_RESULT(const D&, id_<const T&>, id_<const F&>, id_<Ts>...)
+ operator()(Ts&&... xs) const BOOST_HOF_SFINAE_RETURNS
+ (
+ BOOST_HOF_MANGLE_CAST(const D&)(BOOST_HOF_CONST_THIS->get_decorator(xs...))(
+ BOOST_HOF_MANGLE_CAST(const T&)(BOOST_HOF_CONST_THIS->get_data(xs...)),
+ BOOST_HOF_MANGLE_CAST(const F&)(BOOST_HOF_CONST_THIS->base_function(xs...)),
+ BOOST_HOF_FORWARD(Ts)(xs)...
+ )
+ );
+};
+
+template<class D, class T>
+struct decoration
+: compressed_pair<D, T>
+{
+ typedef compressed_pair<D, T> base;
+ BOOST_HOF_INHERIT_CONSTRUCTOR(decoration, base)
+
+ template<class... Ts>
+ constexpr const D& get_decorator(Ts&&... xs) const noexcept
+ {
+ return this->first(xs...);
+ }
+
+ template<class... Ts>
+ constexpr const T& get_data(Ts&&... xs) const noexcept
+ {
+ return this->second(xs...);
+ }
+
+ template<class F>
+ constexpr decorator_invoke<D, T, detail::callable_base<F>> operator()(F f) const
+ BOOST_HOF_NOEXCEPT(BOOST_HOF_IS_NOTHROW_CONSTRUCTIBLE(decorator_invoke<D, T, detail::callable_base<F>>, compressed_pair<D, T>, detail::callable_base<F>&&))
+ {
+ return decorator_invoke<D, T, detail::callable_base<F>>(
+ *this, static_cast<detail::callable_base<F>&&>(f)
+ );
+ }
+};
+
+}
+
+template<class F>
+struct decorate_adaptor : detail::callable_base<F>
+{
+ typedef decorate_adaptor fit_rewritable1_tag;
+ typedef detail::callable_base<F> base;
+ BOOST_HOF_INHERIT_CONSTRUCTOR(decorate_adaptor, detail::callable_base<F>)
+
+ template<class... Ts>
+ constexpr const base& base_function(Ts&&... xs) const noexcept
+ {
+ return boost::hof::always_ref(*this)(xs...);
+ }
+
+ // TODO: Add predicate for constraints
+
+ template<class T>
+ constexpr detail::decoration<base, T> operator()(T x) const
+ BOOST_HOF_NOEXCEPT(BOOST_HOF_IS_NOTHROW_CONSTRUCTIBLE(base, const base&) && BOOST_HOF_IS_NOTHROW_CONSTRUCTIBLE(T, T&&))
+ {
+ return detail::decoration<base, T>(this->base_function(x), static_cast<T&&>(x));
+ }
+
+};
+
+BOOST_HOF_DECLARE_STATIC_VAR(decorate, detail::make<decorate_adaptor>);
+
+}} // namespace boost::hof
+
+#endif