123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657 |
- [/
- Copyright 2007 John Maddock.
- Distributed under the Boost Software License, Version 1.0.
- (See accompanying file LICENSE_1_0.txt or copy at
- http://www.boost.org/LICENSE_1_0.txt).
- ]
- [section:has_trivial_constructor has_trivial_constructor]
- template <class T>
- struct has_trivial_constructor : public __tof {};
-
- template <class T>
- struct has_trivial_default_constructor : public __tof {};
-
- __inherit If T is a (possibly cv-qualified) type with a trivial default-constructor
- then inherits from __true_type, otherwise inherits from __false_type.
- These two traits are synonyms for each other.
- If a type has a trivial default-constructor then the constructor have no effect:
- calls to the constructor can be safely omitted. Note that using meta-programming
- to omit a call to a single trivial-constructor call is of no benefit whatsoever.
- However, if loops and/or exception handling code can also be omitted, then some
- benefit in terms of code size and speed can be obtained.
- __compat Without some (as yet unspecified) help from the compiler,
- has_trivial_constructor will never report that a user-defined class or struct has a
- trivial constructor; this is always safe, if possibly sub-optimal.
- In addition, in order to correctly handle private or deleted default-constructors then
- C++11's `deltype` is required.
- Currently (May 2015) compilers more recent than Visual C++ 8, GCC-4.3, Greenhills 6.0,
- Intel-11.0, and Codegear have the necessary compiler __intrinsics to ensure that this
- trait "just works". You may also test to see if the necessary __intrinsics are available
- by checking to see if the macro `BOOST_HAS_TRIVIAL_CONSTRUCTOR` is defined.
- __std_ref 12.1p6.
- __header ` #include <boost/type_traits/has_trivial_constructor.hpp>` or ` #include <boost/type_traits.hpp>`
- __examples
- [:`has_trivial_constructor<int>` inherits from `__true_type`.]
- [:`has_trivial_constructor<char*>::type` is the type `__true_type`.]
- [:`has_trivial_constructor<int (*)(long)>::value` is an integral constant
- expression that evaluates to /true/.]
- [:`has_trivial_constructor<MyClass>::value` is an integral constant
- expression that evaluates to /false/.]
- [:`has_trivial_constructor<T>::value_type` is the type `bool`.]
- [endsect]
|