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1 | // boost/identifier.hpp ----------------------------------------------------// |
2 | ||
3 | // Copyright Beman Dawes 2006 | |
4 | ||
5 | // Distributed under the Boost Software License, Version 1.0. (See accompanying | |
6 | // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) | |
7 | ||
8 | // See documentation at http://www.boost.org/libs/utility | |
9 | ||
10 | #ifndef BOOST_IDENTIFIER_HPP | |
11 | #define BOOST_IDENTIFIER_HPP | |
12 | ||
13 | #include <boost/utility/enable_if.hpp> | |
14 | #include <boost/type_traits/is_base_of.hpp> | |
15 | #include <iosfwd> | |
16 | ||
17 | namespace boost | |
18 | { | |
19 | namespace detail | |
20 | { | |
21 | // class template identifier ---------------------------------------------// | |
22 | ||
23 | // Always used as a base class so that different instantiations result in | |
24 | // different class types even if instantiated with the same value type T. | |
25 | ||
26 | // Expected usage is that T is often an integer type, best passed by | |
27 | // value. There is no reason why T can't be a possibly larger class such as | |
28 | // std::string, best passed by const reference. | |
29 | ||
30 | // This implementation uses pass by value, based on expected common uses. | |
31 | ||
32 | template <typename T, typename D> | |
33 | class identifier | |
34 | { | |
35 | public: | |
36 | typedef T value_type; | |
37 | ||
38 | const value_type value() const { return m_value; } | |
39 | void assign( value_type v ) { m_value = v; } | |
40 | ||
41 | bool operator==( const D & rhs ) const { return m_value == rhs.m_value; } | |
42 | bool operator!=( const D & rhs ) const { return m_value != rhs.m_value; } | |
43 | bool operator< ( const D & rhs ) const { return m_value < rhs.m_value; } | |
44 | bool operator<=( const D & rhs ) const { return m_value <= rhs.m_value; } | |
45 | bool operator> ( const D & rhs ) const { return m_value > rhs.m_value; } | |
46 | bool operator>=( const D & rhs ) const { return m_value >= rhs.m_value; } | |
47 | ||
48 | typedef void (*unspecified_bool_type)(D); // without the D, unspecified_bool_type | |
49 | static void unspecified_bool_true(D){} // conversion allows relational operators | |
50 | // between different identifier types | |
51 | ||
52 | operator unspecified_bool_type() const { return m_value == value_type() ? 0 : unspecified_bool_true; } | |
53 | bool operator!() const { return m_value == value_type(); } | |
54 | ||
55 | // constructors are protected so that class can only be used as a base class | |
56 | protected: | |
57 | identifier() {} | |
58 | explicit identifier( value_type v ) : m_value(v) {} | |
59 | ||
60 | private: | |
61 | T m_value; | |
62 | }; | |
63 | ||
64 | //#ifndef BOOST_NO_SFINAE | |
65 | ||
66 | // template <class Ostream, class Id> | |
67 | // typename enable_if< is_base_of< identifier< typename Id::value_type, Id >, Id >, | |
68 | // Ostream & >::type operator<<( Ostream & os, const Id & id ) | |
69 | // { | |
70 | // return os << id.value(); | |
71 | // } | |
72 | ||
73 | // template <class Istream, class Id> | |
74 | // typename enable_if< is_base_of< identifier< typename Id::value_type, Id >, Id >, | |
75 | // Istream & >::type operator>>( Istream & is, Id & id ) | |
76 | // { | |
77 | // typename Id::value_type v; | |
78 | // is >> v; | |
79 | // id.value( v ); | |
80 | // return is; | |
81 | // } | |
82 | //#endif | |
83 | ||
84 | } // namespace detail | |
85 | } // namespace boost | |
86 | ||
87 | #endif // BOOST_IDENTIFIER_HPP |