1 //-----------------------------------------------------------------------------
2 // boost blank.hpp header file
3 // See http://www.boost.org for updates, documentation, and revision history.
4 //-----------------------------------------------------------------------------
5 //
6 // Copyright (c) 2003
7 // Eric Friedman
8 //
9 // Distributed under the Boost Software License, Version 1.0. (See
10 // accompanying file LICENSE_1_0.txt or copy at
11 // http://www.boost.org/LICENSE_1_0.txt)
12
13 #ifndef BOOST_BLANK_HPP
14 #define BOOST_BLANK_HPP
15
16 #include "boost/blank_fwd.hpp"
17
18 #include <iosfwd> // for std::basic_ostream forward declare
19
20 #include "boost/detail/templated_streams.hpp"
21 #include "boost/mpl/bool.hpp"
22 #include "boost/type_traits/is_empty.hpp"
23 #include "boost/type_traits/is_pod.hpp"
24 #include "boost/type_traits/is_stateless.hpp"
25
26 namespace boost {
27
28 struct blank
29 {
30 };
31
32 // type traits specializations
33 //
34
35 template <>
36 struct is_pod< blank >
37 : mpl::true_
38 {
39 };
40
41 template <>
42 struct is_empty< blank >
43 : mpl::true_
44 {
45 };
46
47 template <>
48 struct is_stateless< blank >
49 : mpl::true_
50 {
51 };
52
53 // relational operators
54 //
55
operator ==(const blank &,const blank &)56 inline bool operator==(const blank&, const blank&)
57 {
58 return true;
59 }
60
operator <(const blank &,const blank &)61 inline bool operator<(const blank&, const blank&)
62 {
63 return false;
64 }
65
66 // streaming support
67 //
68 BOOST_TEMPLATED_STREAM_TEMPLATE(E,T)
69 inline BOOST_TEMPLATED_STREAM(ostream, E,T)& operator<<(
70 BOOST_TEMPLATED_STREAM(ostream, E,T)& out
71 , const blank&
72 )
73 {
74 // (output nothing)
75 return out;
76 }
77
78 } // namespace boost
79
80 #endif // BOOST_BLANK_HPP
81