+The template initialized
+offers both value-initialization and direct-initialization.
+It is especially useful as a data member type, allowing the very same object
+to be either direct-initialized or value-initialized.
+
The const object initialized_value
allows value-initializing a variable as follows:
@@ -340,6 +347,52 @@
value_initialized<int> x ;
get(x) = 1 ; // OK
value_initialized<int const> cx ;
get(x) = 1 ; // ERROR: Cannot modify a const object
value_initialized<int> const x_c ;
get(x_c) = 1 ; // ERROR: Cannot modify a const object
value_initialized<int const> const cx_c ;
get(cx_c) = 1 ; // ERROR: Cannot modify a const object
+template class initialized<T>
+
+namespace boost {
template<class T>
class initialized
{
+
public :
+
initialized() : x() {}
+
explicit initialized(T const & arg) : x(arg) {}
+
operator T const &() const;
+
operator T&();
+
T const &data() const;
+
T& data();
+
void swap( value_initialized<T>& );
+
+
private :
+
unspecified x ;
+
} ;
+
+
template<class T>
+
T const& get ( initialized<T> const& x );
+
+
template<class T>
+
T& get ( initialized<T>& x );
+
+
} // namespace boost
+
+
+The template class boost::initialized<T> supports both value-initialization
+and direct-initialization, so its interface is a superset of the interface
+of value_initialized<T>: Its default-constructor
+value-initializes the wrapped object just like the default-constructor of
+value_initialized<T>, but boost::initialized<T>
+also offers an extra explicit
+constructor, which direct-initializes the wrapped object by the specified value.
+
+
+initialized<T> is especially useful when the wrapped
+object must be either value-initialized or direct-initialized, depending on
+runtime conditions. For example, initialized<T> could
+hold the value of a data member that may be value-initialized by some
+constructors, and direct-initialized by others.
+On the other hand, if it is known beforehand that the
+object must always be value-initialized, value_initialized<T>
+may be preferable. And if the object must always be
+direct-initialized, none of the two wrappers really needs to be used.
+
+
+
initialized_value
@@ -399,6 +452,9 @@
value_initialized was reimplemented by Fernando Cacciola and Niels Dekker
for Boost release version 1.35 (2008), offering a workaround to various compiler issues.
+boost::initialized was very much inspired by feedback from Edward Diener and
+ Jeffrey Hellrung.
+
initialized_value was written by Niels Dekker, and added to Boost release version 1.36 (2008).
Developed by Fernando Cacciola,
@@ -407,9 +463,9 @@
-Revised 03 October 2009
+Revised 1 May 2010
-© Copyright Fernando Cacciola, 2002, 2009.
+© Copyright Fernando Cacciola, 2002 - 2010.
Distributed under the Boost Software License, Version 1.0. See
www.boost.org/LICENSE_1_0.txt