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- [/
- / Copyright (c) 2001, 2002, 2006 Peter Dimov
- / Copyright (c) 2002 David Abrahams
- / Copyright (c) 2002 Aleksey Gurtovoy
- / Copyright (c) 2003, 2004 Douglas Gregor
- / Copyright (c) 2009 Ronald Garcia
- / Copyright (c) 2014 Glen Joseph Fernandes
- /
- / 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:ref ref]
- [simplesect Authors]
- * Jaakko J\u00E4rvi
- * Peter Dimov
- * Douglas Gregor
- * Dave Abrahams
- * Frank Mori Hess
- * Ronald Garcia
- [endsimplesect]
- [section Introduction]
- The Ref library is a small library that is useful for passing
- references to function templates (algorithms) that would
- usually take copies of their arguments. It defines the class
- template `boost::reference_wrapper<T>`, two functions
- `boost::ref` and `boost::cref` that return instances of
- `boost::reference_wrapper<T>`, a function `boost::unwrap_ref`
- that unwraps a `boost::reference_wrapper<T>` or returns a
- reference to any other type of object, and the two traits
- classes `boost::is_reference_wrapper<T>` and
- `boost::unwrap_reference<T>`.
- The purpose of `boost::reference_wrapper<T>` is to contain a
- reference to an object of type `T`. It is primarily used to
- "feed" references to function templates (algorithms) that take
- their parameter by value.
- To support this usage, `boost::reference_wrapper<T>` provides
- an implicit conversion to `T&`. This usually allows the
- function templates to work on references unmodified.
- `boost::reference_wrapper<T>` is both CopyConstructible and
- Assignable (ordinary references are not Assignable).
- The `expression boost::ref(x)` returns a
- `boost::reference_wrapper<X>(x)` where `X` is the type of `x`.
- Similarly, `boost::cref(x)` returns a
- `boost::reference_wrapper<X const>(x)`.
- The expression `boost::unwrap_ref(x)` returns a
- `boost::unwrap_reference<X>::type&` where `X` is the type of
- `x`.
- The expression `boost::is_reference_wrapper<T>::value` is
- `true` if `T` is a `reference_wrapper`, and `false` otherwise.
- The type-expression `boost::unwrap_reference<T>::type` is
- `T::type` if `T` is a `reference_wrapper`, `T` otherwise.
- [endsect]
- [xinclude ref_reference.xml]
- [section Acknowledgments]
- `ref` and `cref` were originally part of the Tuple library by
- Jaakko J\u00E4rvi. They were "promoted to `boost::` status" by
- Peter Dimov because they are generally useful. Douglas Gregor
- and Dave Abrahams contributed `is_reference_wrapper` and
- `unwrap_reference`. Frank Mori Hess and Ronald Garcia
- contributed `boost::unwrap_ref`.
- [endsect]
- [endsect]
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