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 #if !defined(BOOST_NO_IOSTREAM)
19 #include <iosfwd> // for std::basic_ostream forward declare
20 #include "boost/detail/templated_streams.hpp"
21 #endif // BOOST_NO_IOSTREAM
22
23 #include "boost/type_traits/integral_constant.hpp"
24 #include "boost/type_traits/is_empty.hpp"
25 #include "boost/type_traits/is_pod.hpp"
26 #include "boost/type_traits/is_stateless.hpp"
27
28 namespace boost {
29
30 struct blank
31 {
32 };
33
34 // type traits specializations
35 //
36
37 template <>
38 struct is_pod< blank >
39 : boost::true_type
40 {
41 };
42
43 template <>
44 struct is_empty< blank >
45 : boost::true_type
46 {
47 };
48
49 template <>
50 struct is_stateless< blank >
51 : boost::true_type
52 {
53 };
54
55 // relational operators
56 //
57
operator ==(const blank &,const blank &)58 inline bool operator==(const blank&, const blank&)
59 {
60 return true;
61 }
62
operator <=(const blank &,const blank &)63 inline bool operator<=(const blank&, const blank&)
64 {
65 return true;
66 }
67
operator >=(const blank &,const blank &)68 inline bool operator>=(const blank&, const blank&)
69 {
70 return true;
71 }
72
operator !=(const blank &,const blank &)73 inline bool operator!=(const blank&, const blank&)
74 {
75 return false;
76 }
77
operator <(const blank &,const blank &)78 inline bool operator<(const blank&, const blank&)
79 {
80 return false;
81 }
82
operator >(const blank &,const blank &)83 inline bool operator>(const blank&, const blank&)
84 {
85 return false;
86 }
87
88 // streaming support
89 //
90 #if !defined(BOOST_NO_IOSTREAM)
91
92 BOOST_TEMPLATED_STREAM_TEMPLATE(E,T)
93 inline BOOST_TEMPLATED_STREAM(ostream, E,T)& operator<<(
94 BOOST_TEMPLATED_STREAM(ostream, E,T)& out
95 , const blank&
96 )
97 {
98 // (output nothing)
99 return out;
100 }
101
102 #endif // BOOST_NO_IOSTREAM
103
104 } // namespace boost
105
106 #endif // BOOST_BLANK_HPP
107