ceph/src/boost/libs/type_traits/doc/has_trivial_constructor.qbk

   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