1///////////////////////////////////////////////////////////////////////////////
2// reference_accumulator.hpp
3//
4// Copyright 2005 Eric Niebler. Distributed under the Boost
5// Software License, Version 1.0. (See accompanying file
6// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
7
8#ifndef BOOST_ACCUMULATORS_FRAMEWORK_ACCUMULATORS_REFERENCE_ACCUMULATOR_HPP_EAN_03_23_2006
9#define BOOST_ACCUMULATORS_FRAMEWORK_ACCUMULATORS_REFERENCE_ACCUMULATOR_HPP_EAN_03_23_2006
10
11#include <boost/ref.hpp>
12#include <boost/mpl/always.hpp>
13#include <boost/parameter/keyword.hpp>
14#include <boost/accumulators/framework/depends_on.hpp> // for feature_tag
15#include <boost/accumulators/framework/accumulator_base.hpp>
16#include <boost/accumulators/framework/extractor.hpp>
17
18namespace boost { namespace accumulators
19{
20
21namespace impl
22{
23 //////////////////////////////////////////////////////////////////////////
24 // reference_accumulator_impl
25 //
26 template<typename Referent, typename Tag>
27 struct reference_accumulator_impl
28 : accumulator_base
29 {
30 typedef Referent &result_type;
31
32 template<typename Args>
33 reference_accumulator_impl(Args const &args)
34 : ref(args[parameter::keyword<Tag>::instance])
35 {
36 }
37
38 result_type result(dont_care) const
39 {
40 return this->ref;
41 }
42
43 private:
44 reference_wrapper<Referent> ref;
45 };
46} // namespace impl
47
48namespace tag
49{
50 //////////////////////////////////////////////////////////////////////////
51 // reference_tag
52 template<typename Tag>
53 struct reference_tag
54 {
55 };
56
57 //////////////////////////////////////////////////////////////////////////
58 // reference
59 template<typename Referent, typename Tag>
60 struct reference
61 : depends_on<>
62 {
63 /// INTERNAL ONLY
64 ///
65 typedef mpl::always<accumulators::impl::reference_accumulator_impl<Referent, Tag> > impl;
66 };
67}
68
69namespace extract
70{
71 BOOST_ACCUMULATORS_DEFINE_EXTRACTOR(tag, reference, (typename)(typename))
72 BOOST_ACCUMULATORS_DEFINE_EXTRACTOR(tag, reference_tag, (typename))
73}
74
75using extract::reference;
76using extract::reference_tag;
77
78// Map all reference<V,T> features to reference_tag<T> so
79// that references can be extracted using reference_tag<T>
80// without specifying the referent type.
81template<typename ValueType, typename Tag>
82struct feature_of<tag::reference<ValueType, Tag> >
83 : feature_of<tag::reference_tag<Tag> >
84{
85};
86
87}} // namespace boost::accumulators
88
89#endif
90

source code of include/boost/accumulators/framework/accumulators/reference_accumulator.hpp