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1 | [/ |
2 | Copyright 2007 John Maddock. | |
3 | Distributed under the Boost Software License, Version 1.0. | |
4 | (See accompanying file LICENSE_1_0.txt or copy at | |
5 | http://www.boost.org/LICENSE_1_0.txt). | |
6 | ] | |
7 | ||
8 | [section:has_trivial_constructor has_trivial_constructor] | |
9 | ||
10 | template <class T> | |
11 | struct has_trivial_constructor : public __tof {}; | |
12 | ||
13 | template <class T> | |
14 | struct has_trivial_default_constructor : public __tof {}; | |
15 | ||
16 | __inherit If T is a (possibly cv-qualified) type with a trivial default-constructor | |
17 | then inherits from __true_type, otherwise inherits from __false_type. | |
18 | ||
19 | These two traits are synonyms for each other. | |
20 | ||
21 | If a type has a trivial default-constructor then the constructor have no effect: | |
22 | calls to the constructor can be safely omitted. Note that using meta-programming | |
23 | to omit a call to a single trivial-constructor call is of no benefit whatsoever. | |
24 | However, if loops and/or exception handling code can also be omitted, then some | |
25 | benefit in terms of code size and speed can be obtained. | |
26 | ||
27 | __compat Without some (as yet unspecified) help from the compiler, | |
28 | has_trivial_constructor will never report that a user-defined class or struct has a | |
29 | trivial constructor; this is always safe, if possibly sub-optimal. | |
30 | In addition, in order to correctly handle private or deleted default-constructors then | |
31 | C++11's `deltype` is required. | |
32 | Currently (May 2015) compilers more recent than Visual C++ 8, GCC-4.3, Greenhills 6.0, | |
33 | Intel-11.0, and Codegear have the necessary compiler __intrinsics to ensure that this | |
34 | trait "just works". You may also test to see if the necessary __intrinsics are available | |
35 | by checking to see if the macro `BOOST_HAS_TRIVIAL_CONSTRUCTOR` is defined. | |
36 | ||
37 | ||
38 | __std_ref 12.1p6. | |
39 | ||
40 | __header ` #include <boost/type_traits/has_trivial_constructor.hpp>` or ` #include <boost/type_traits.hpp>` | |
41 | ||
42 | __examples | |
43 | ||
44 | [:`has_trivial_constructor<int>` inherits from `__true_type`.] | |
45 | ||
46 | [:`has_trivial_constructor<char*>::type` is the type `__true_type`.] | |
47 | ||
48 | [:`has_trivial_constructor<int (*)(long)>::value` is an integral constant | |
49 | expression that evaluates to /true/.] | |
50 | ||
51 | [:`has_trivial_constructor<MyClass>::value` is an integral constant | |
52 | expression that evaluates to /false/.] | |
53 | ||
54 | [:`has_trivial_constructor<T>::value_type` is the type `bool`.] | |
55 | ||
56 | [endsect] | |
57 |