83 lines
2.5 KiB
Plaintext
83 lines
2.5 KiB
Plaintext
[/
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/ Copyright (c) 2001, 2002, 2006 Peter Dimov
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/ Copyright (c) 2002 David Abrahams
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/ Copyright (c) 2002 Aleksey Gurtovoy
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/ Copyright (c) 2003, 2004 Douglas Gregor
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/ Copyright (c) 2009 Ronald Garcia
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/ Copyright (c) 2014 Glen Joseph Fernandes
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/
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/ Distributed under the Boost Software License, Version 1.0. (See
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/ accompanying file LICENSE_1_0.txt or copy at
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/ http://www.boost.org/LICENSE_1_0.txt)
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/]
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[section:ref ref]
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[simplesect Authors]
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* Jaakko J\u00E4rvi
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* Peter Dimov
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* Douglas Gregor
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* Dave Abrahams
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* Frank Mori Hess
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* Ronald Garcia
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[endsimplesect]
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[section Introduction]
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The Ref library is a small library that is useful for passing
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references to function templates (algorithms) that would
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usually take copies of their arguments. It defines the class
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template `boost::reference_wrapper<T>`, two functions
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`boost::ref` and `boost::cref` that return instances of
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`boost::reference_wrapper<T>`, a function `boost::unwrap_ref`
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that unwraps a `boost::reference_wrapper<T>` or returns a
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reference to any other type of object, and the two traits
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classes `boost::is_reference_wrapper<T>` and
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`boost::unwrap_reference<T>`.
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The purpose of `boost::reference_wrapper<T>` is to contain a
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reference to an object of type `T`. It is primarily used to
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"feed" references to function templates (algorithms) that take
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their parameter by value.
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To support this usage, `boost::reference_wrapper<T>` provides
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an implicit conversion to `T&`. This usually allows the
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function templates to work on references unmodified.
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`boost::reference_wrapper<T>` is both CopyConstructible and
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Assignable (ordinary references are not Assignable).
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The `expression boost::ref(x)` returns a
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`boost::reference_wrapper<X>(x)` where `X` is the type of `x`.
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Similarly, `boost::cref(x)` returns a
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`boost::reference_wrapper<X const>(x)`.
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The expression `boost::unwrap_ref(x)` returns a
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`boost::unwrap_reference<X>::type&` where `X` is the type of
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`x`.
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The expression `boost::is_reference_wrapper<T>::value` is
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`true` if `T` is a `reference_wrapper`, and `false` otherwise.
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The type-expression `boost::unwrap_reference<T>::type` is
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`T::type` if `T` is a `reference_wrapper`, `T` otherwise.
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[endsect]
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[xinclude ref_reference.xml]
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[section Acknowledgments]
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`ref` and `cref` were originally part of the Tuple library by
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Jaakko J\u00E4rvi. They were "promoted to `boost::` status" by
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Peter Dimov because they are generally useful. Douglas Gregor
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and Dave Abrahams contributed `is_reference_wrapper` and
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`unwrap_reference`. Frank Mori Hess and Ronald Garcia
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contributed `boost::unwrap_ref`.
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[endsect]
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[endsect]
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