1 /*=============================================================================
2     Copyright (c) 2014 Paul Fultz II
3     mutable.h
4     Distributed under the Boost Software License, Version 1.0. (See accompanying
5     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
6 ==============================================================================*/
7 
8 #ifndef BOOST_HOF_GUARD_FUNCTION_MUTABLE_H
9 #define BOOST_HOF_GUARD_FUNCTION_MUTABLE_H
10 
11 /// mutable
12 /// =======
13 ///
14 /// Description
15 /// -----------
16 ///
17 /// The `mutable` function adaptor allows using a non-const function object
18 /// inside of a const-function object. In Fit, all the function adaptors use
19 /// `const` call overloads, so if there is a function that has a non-const
20 /// call operator, it couldn't be used directly. So, `mutable_` allows the
21 /// function to be used inside of the call operator.
22 ///
23 /// NOTE: This function should be used with caution since many functions are
24 /// copied, so relying on some internal shared state can be error-prone.
25 ///
26 /// Synopsis
27 /// --------
28 ///
29 ///     template<class F>
30 ///     mutable_adaptor<F> mutable_(F f)
31 ///
32 /// Requirements
33 /// ------------
34 ///
35 /// F must be:
36 ///
37 /// * [MutableFunctionObject](MutableFunctionObject)
38 /// * MoveConstructible
39 ///
40 
41 #include <boost/hof/detail/result_of.hpp>
42 #include <boost/hof/detail/delegate.hpp>
43 #include <boost/hof/detail/move.hpp>
44 #include <boost/hof/detail/make.hpp>
45 #include <boost/hof/detail/static_const_var.hpp>
46 
47 namespace boost { namespace hof {
48 
49 template<class F>
50 struct mutable_adaptor
51 {
52     mutable F f;
53 
54     BOOST_HOF_DELEGATE_CONSTRUCTOR(mutable_adaptor, F, f);
55 
56     BOOST_HOF_RETURNS_CLASS(mutable_adaptor);
57 
58     template<class... Ts>
59     BOOST_HOF_SFINAE_RESULT(F, id_<Ts>...)
60     operator()(Ts&&... xs) const BOOST_HOF_SFINAE_RETURNS(BOOST_HOF_CONST_THIS->f(BOOST_HOF_FORWARD(Ts)(xs)...));
61 };
62 
63 BOOST_HOF_DECLARE_STATIC_VAR(mutable_, detail::make<mutable_adaptor>);
64 
65 }} // namespace boost::hof
66 
67 
68 #endif
69