1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
|
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE header PUBLIC "-//Boost//DTD BoostBook XML V1.0//EN"
"http://www.boost.org/tools/boostbook/dtd/boostbook.dtd">
<header name="boost/variant/get.hpp">
<namespace name="boost">
<class name="bad_get">
<inherit access="public">
<classname>std::exception</classname>
</inherit>
<purpose>
<simpara>The exception thrown in the event of a failed application of
<code><functionname>boost::get</functionname></code> on the given
operand value.</simpara>
</purpose>
<method name="what" specifiers="virtual" cv="const">
<type>const char *</type>
</method>
</class>
<overloaded-function name="get">
<signature>
<template>
<template-type-parameter name="U"/>
<template-type-parameter name="T1"/>
<template-type-parameter name="T2"/>
<template-varargs/>
<template-type-parameter name="TN"/>
</template>
<type>U *</type>
<parameter name="operand">
<paramtype><classname>variant</classname><T1, T2, ..., TN> *</paramtype>
</parameter>
</signature>
<signature>
<template>
<template-type-parameter name="U"/>
<template-type-parameter name="T1"/>
<template-type-parameter name="T2"/>
<template-varargs/>
<template-type-parameter name="TN"/>
</template>
<type>const U *</type>
<parameter name="operand">
<paramtype>const <classname>variant</classname><T1, T2, ..., TN> *</paramtype>
</parameter>
</signature>
<signature>
<template>
<template-type-parameter name="U"/>
<template-type-parameter name="T1"/>
<template-type-parameter name="T2"/>
<template-varargs/>
<template-type-parameter name="TN"/>
</template>
<type>U &</type>
<parameter name="operand">
<paramtype><classname>variant</classname><T1, T2, ..., TN> &</paramtype>
</parameter>
</signature>
<signature>
<template>
<template-type-parameter name="U"/>
<template-type-parameter name="T1"/>
<template-type-parameter name="T2"/>
<template-varargs/>
<template-type-parameter name="TN"/>
</template>
<type>const U &</type>
<parameter name="operand">
<paramtype>const <classname>variant</classname><T1, T2, ..., TN> &</paramtype>
</parameter>
</signature>
<purpose>
<simpara>Retrieves a value of a specified type from a given
<code><classname>variant</classname></code>.</simpara>
</purpose>
<description>
<simpara>The <code>get</code> function allows run-time checked,
type-safe retrieval of the content of the given
<code><classname>variant</classname></code>. The function succeeds
only if the content is of the specified type <code>U</code>, with
failure indicated as described below.</simpara>
<simpara><emphasis role="bold">Warning</emphasis>: After either
<code>operand</code> or its content is destroyed (e.g., when the
given <code><classname>variant</classname></code> is assigned a
value of different type), the returned reference is invalidated.
Thus, significant care and caution must be extended when handling
the returned reference.</simpara>
</description>
<notes>
<simpara>As part of its guarantee of type-safety, <code>get</code>
enforces <code>const</code>-correctness. Thus, the specified type
<code>U</code> must be <code>const</code>-qualified whenever
<code>operand</code> or its content is likewise
<code>const</code>-qualified. The converse, however, is not required:
that is, the specified type <code>U</code> may be
<code>const</code>-qualified even when <code>operand</code> and its
content are not.</simpara>
</notes>
<returns>
<simpara>If passed a pointer, <code>get</code> returns a pointer to
the value content if it is of the specified type <code>U</code>;
otherwise, a null pointer is returned. If passed a reference,
<code>get</code> returns a reference to the value content if it is of
the specified type <code>U</code>; otherwise, an exception is thrown
(see below).</simpara>
</returns>
<throws>
<simpara>Overloads taking a
<code><classname>variant</classname></code> pointer will not
throw; the overloads taking a
<code><classname>variant</classname></code> reference throw
<code><classname>bad_get</classname></code> if the content is not of
the specified type <code>U</code>.</simpara>
</throws>
<rationale>
<simpara>While visitation via
<code><functionname>apply_visitor</functionname></code>
is generally preferred due to its greater safety, <code>get</code> may
may be more convenient in some cases due to its straightforward
usage.</simpara>
</rationale>
</overloaded-function>
</namespace>
</header>
|
