Boost C++ Libraries

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has_trivial_constructor

template <class T>
struct has_trivial_constructor : public true_type-or-false_type {};

template <class T>
struct has_trivial_default_constructor : public true_type-or-false_type {};

Inherits: 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.

Compiler Compatibility: If the compiler does not support partial-specialization of class templates, then this template can not be used with function types.

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. Currently (May 2005) only MWCW 9 and Visual C++ 8 have the necessary compiler intrinsics to detect user-defined classes with trivial constructors.

C++ Standard Reference: 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.


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