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< span class = "keyword" > class< / span > < span class = "identifier" > none_t< / span > < span class = "special" > {/*< / span > < span class = "identifier" > see< / span > < span class = "identifier" > below< / span > < span class = "special" > */};< / span >
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< span class = "keyword" > inline< / span > < span class = "keyword" > constexpr< / span > < span class = "identifier" > none_t< / span > < span class = "identifier" > none< / span > < span class = "special" > (/*< / span > < span class = "identifier" > see< / span > < span class = "identifier" > below< / span > < span class = "special" > */);< / span >
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< span class = "special" > }< / span > < span class = "comment" > // namespace boost< / span >
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Class < code class = "computeroutput" > < span class = "identifier" > none_t< / span > < / code > is meant to
serve as a tag for selecting appropriate overloads of from < code class = "computeroutput" > < span class = "identifier" > optional< / span > < / code > 's interface. It is an empty,
trivially copyable class with disabled default constructor.
< / p >
< p >
Constant < code class = "computeroutput" > < span class = "identifier" > none< / span > < / code > is used to
indicate an optional object that does not contain a value in initialization,
assignment and relational operations of < code class = "computeroutput" > < span class = "identifier" > optional< / span > < / code > .
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< td align = "right" > < div class = "copyright-footer" > Copyright © 2003-2007 Fernando Luis Cacciola Carballal< br > Copyright © 2014-2021 Andrzej Krzemieński< p >
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Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at < a href = "http://www.boost.org/LICENSE_1_0.txt" target = "_top" > http://www.boost.org/LICENSE_1_0.txt< / a > )
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