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< a name = "boost_optional.exception_safety_guarantees" > < / a > < a class = "link" href = "exception_safety_guarantees.html" title = "Exception Safety Guarantees" > Exception Safety
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Guarantees< / a >
< / h2 > < / div > < / div > < / div >
< p >
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Because of the current implementation (see < a class = "link" href = "implementation_notes.html" title = "Implementation Notes" > Implementation
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Notes< / a > ), all of the assignment methods:
< / p >
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< div class = "itemizedlist" > < ul class = "itemizedlist" style = "list-style-type: disc; " >
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< li class = "listitem" >
< code class = "computeroutput" > < span class = "identifier" > optional< / span > < span class = "special" > < < / span > < span class = "identifier" > T< / span > < span class = "special" > > ::< / span > < span class = "keyword" > operator< / span > < span class = "special" > =< / span > < span class = "special" > (< / span > < span class = "identifier" > optional< / span > < span class = "special" > < < / span > < span class = "identifier" > T< / span > < span class = "special" > > < / span > < span class = "keyword" > const< / span > < span class = "special" > & < / span > < span class = "special" > )< / span > < / code >
< / li >
< li class = "listitem" >
< code class = "computeroutput" > < span class = "identifier" > optional< / span > < span class = "special" > < < / span > < span class = "identifier" > T< / span > < span class = "special" > > ::< / span > < span class = "keyword" > operator< / span > < span class = "special" > =< / span > < span class = "special" > (< / span > < span class = "identifier" > T< / span > < span class = "keyword" > const< / span > < span class = "special" > & < / span > < span class = "special" > )< / span > < / code >
< / li >
< li class = "listitem" >
< code class = "computeroutput" > < span class = "keyword" > template< / span > < span class = "special" > < < / span > < span class = "keyword" > class< / span > < span class = "identifier" > U< / span > < span class = "special" > > < / span > < span class = "identifier" > optional< / span > < span class = "special" > < < / span > < span class = "identifier" > T< / span > < span class = "special" > > ::< / span > < span class = "keyword" > operator< / span > < span class = "special" > =< / span > < span class = "special" > (< / span > < span class = "identifier" > optional< / span > < span class = "special" > < < / span > < span class = "identifier" > U< / span > < span class = "special" > > < / span > < span class = "keyword" > const< / span > < span class = "special" > & < / span > < span class = "special" > )< / span > < / code >
< / li >
< li class = "listitem" >
< code class = "computeroutput" > < span class = "keyword" > template< / span > < span class = "special" > < < / span > < span class = "keyword" > class< / span > < span class = "identifier" > InPlaceFactory< / span > < span class = "special" > > < / span > < span class = "identifier" > optional< / span > < span class = "special" > < < / span > < span class = "identifier" > T< / span > < span class = "special" > > ::< / span > < span class = "keyword" > operator< / span > < span class = "special" > =< / span > < span class = "special" > (< / span > < span class = "identifier" > InPlaceFactory< / span >
< span class = "keyword" > const< / span > < span class = "special" > & < / span >
< span class = "special" > )< / span > < / code >
< / li >
< li class = "listitem" >
< code class = "computeroutput" > < span class = "keyword" > template< / span > < span class = "special" > < < / span > < span class = "keyword" > class< / span > < span class = "identifier" > TypedInPlaceFactory< / span > < span class = "special" > > < / span > < span class = "identifier" > optional< / span > < span class = "special" > < < / span > < span class = "identifier" > T< / span > < span class = "special" > > ::< / span > < span class = "keyword" > operator< / span > < span class = "special" > =< / span > < span class = "special" > (< / span > < span class = "identifier" > TypedInPlaceFactory< / span >
< span class = "keyword" > const< / span > < span class = "special" > & < / span >
< span class = "special" > )< / span > < / code >
< / li >
< li class = "listitem" >
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< code class = "computeroutput" > < span class = "identifier" > optional< / span > < span class = "special" > < < / span > < span class = "identifier" > T< / span > < span class = "special" > > ::< / span > < span class = "identifier" > reset< / span > < span class = "special" > (< / span > < span class = "identifier" > T< / span > < span class = "keyword" > const< / span > < span class = "special" > & )< / span > < / code >
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< / li >
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< / ul > < / div >
< p >
Can only < span class = "emphasis" > < em > guarantee< / em > < / span > the < span class = "underline" > basic
exception safety< / span > : The lvalue optional is left < span class = "underline" > uninitialized< / span >
if an exception is thrown (any previous value is < span class = "emphasis" > < em > first< / em > < / span >
destroyed using < code class = "computeroutput" > < span class = "identifier" > T< / span > < span class = "special" > ::~< / span > < span class = "identifier" > T< / span > < span class = "special" > ()< / span > < / code > )
< / p >
< p >
On the other hand, the < span class = "emphasis" > < em > uninitializing< / em > < / span > methods:
< / p >
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< div class = "itemizedlist" > < ul class = "itemizedlist" style = "list-style-type: disc; " >
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< li class = "listitem" >
< code class = "computeroutput" > < span class = "identifier" > optional< / span > < span class = "special" > < < / span > < span class = "identifier" > T< / span > < span class = "special" > > ::< / span > < span class = "keyword" > operator< / span > < span class = "special" > =< / span > < span class = "special" > (< / span > < span class = "identifier" > detail< / span > < span class = "special" > ::< / span > < span class = "identifier" > none_t< / span > < span class = "special" > )< / span > < / code >
< / li >
< li class = "listitem" >
< code class = "computeroutput" > < span class = "identifier" > optional< / span > < span class = "special" > < < / span > < span class = "identifier" > T< / span > < span class = "special" > > ::< / span > < span class = "identifier" > reset< / span > < span class = "special" > ()< / span > < / code >
< / li >
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< / ul > < / div >
< p >
Provide the no-throw guarantee (assuming a no-throw < code class = "computeroutput" > < span class = "identifier" > T< / span > < span class = "special" > ::~< / span > < span class = "identifier" > T< / span > < span class = "special" > ()< / span > < / code > )
< / p >
< p >
However, since < code class = "computeroutput" > < span class = "identifier" > optional< / span > < span class = "special" > < > < / span > < / code >
itself doesn't throw any exceptions, the only source for exceptions here are
< code class = "computeroutput" > < span class = "identifier" > T< / span > < / code > 's constructor, so if you
know the exception guarantees for < code class = "computeroutput" > < span class = "identifier" > T< / span > < span class = "special" > ::< / span > < span class = "identifier" > T< / span > < span class = "special" > (< / span >
< span class = "identifier" > T< / span > < span class = "keyword" > const< / span > < span class = "special" > & < / span > < span class = "special" > )< / span > < / code > , you
know that < code class = "computeroutput" > < span class = "identifier" > optional< / span > < / code > 's assignment
and reset has the same guarantees.
< / p >
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< pre class = "programlisting" > < span class = "comment" > //< / span >
< span class = "comment" > // Case 1: Exception thrown during assignment.< / span >
< span class = "comment" > //< / span >
< span class = "identifier" > T< / span > < span class = "identifier" > v0< / span > < span class = "special" > (< / span > < span class = "number" > 123< / span > < span class = "special" > );< / span >
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< span class = "identifier" > optional< / span > < span class = "special" > < < / span > < span class = "identifier" > T< / span > < span class = "special" > > < / span > < span class = "identifier" > opt0< / span > < span class = "special" > (< / span > < span class = "identifier" > v0< / span > < span class = "special" > );< / span >
< span class = "keyword" > try< / span >
< span class = "special" > {< / span >
< span class = "identifier" > T< / span > < span class = "identifier" > v1< / span > < span class = "special" > (< / span > < span class = "number" > 456< / span > < span class = "special" > );< / span >
< span class = "identifier" > optional< / span > < span class = "special" > < < / span > < span class = "identifier" > T< / span > < span class = "special" > > < / span > < span class = "identifier" > opt1< / span > < span class = "special" > (< / span > < span class = "identifier" > v1< / span > < span class = "special" > );< / span >
< span class = "identifier" > opt0< / span > < span class = "special" > =< / span > < span class = "identifier" > opt1< / span > < span class = "special" > ;< / span >
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< span class = "comment" > // If no exception was thrown, assignment succeeded.< / span >
< span class = "identifier" > assert< / span > < span class = "special" > (< / span > < span class = "special" > *< / span > < span class = "identifier" > opt0< / span > < span class = "special" > ==< / span > < span class = "identifier" > v1< / span > < span class = "special" > )< / span > < span class = "special" > ;< / span >
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< span class = "special" > }< / span >
< span class = "keyword" > catch< / span > < span class = "special" > (...)< / span >
< span class = "special" > {< / span >
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< span class = "comment" > // If any exception was thrown, 'opt0' is reset to uninitialized.< / span >
< span class = "identifier" > assert< / span > < span class = "special" > (< / span > < span class = "special" > !< / span > < span class = "identifier" > opt0< / span > < span class = "special" > )< / span > < span class = "special" > ;< / span >
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< span class = "special" > }< / span >
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< span class = "comment" > //< / span >
< span class = "comment" > // Case 2: Exception thrown during reset(v)< / span >
< span class = "comment" > //< / span >
< span class = "identifier" > T< / span > < span class = "identifier" > v0< / span > < span class = "special" > (< / span > < span class = "number" > 123< / span > < span class = "special" > );< / span >
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< span class = "identifier" > optional< / span > < span class = "special" > < < / span > < span class = "identifier" > T< / span > < span class = "special" > > < / span > < span class = "identifier" > opt< / span > < span class = "special" > (< / span > < span class = "identifier" > v0< / span > < span class = "special" > );< / span >
< span class = "keyword" > try< / span >
< span class = "special" > {< / span >
< span class = "identifier" > T< / span > < span class = "identifier" > v1< / span > < span class = "special" > (< / span > < span class = "number" > 456< / span > < span class = "special" > );< / span >
< span class = "identifier" > opt< / span > < span class = "special" > .< / span > < span class = "identifier" > reset< / span > < span class = "special" > (< / span > < span class = "identifier" > v1< / span > < span class = "special" > )< / span > < span class = "special" > ;< / span >
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< span class = "comment" > // If no exception was thrown, reset succeeded.< / span >
< span class = "identifier" > assert< / span > < span class = "special" > (< / span > < span class = "special" > *< / span > < span class = "identifier" > opt< / span > < span class = "special" > ==< / span > < span class = "identifier" > v1< / span > < span class = "special" > )< / span > < span class = "special" > ;< / span >
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< span class = "special" > }< / span >
< span class = "keyword" > catch< / span > < span class = "special" > (...)< / span >
< span class = "special" > {< / span >
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< span class = "comment" > // If any exception was thrown, 'opt' is reset to uninitialized.< / span >
< span class = "identifier" > assert< / span > < span class = "special" > (< / span > < span class = "special" > !< / span > < span class = "identifier" > opt< / span > < span class = "special" > )< / span > < span class = "special" > ;< / span >
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< span class = "special" > }< / span >
< / pre >
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< h4 >
< a name = "boost_optional.exception_safety_guarantees.h0" > < / a >
< span class = "phrase" > < a name = "boost_optional.exception_safety_guarantees.swap" > < / a > < / span > < a class = "link" href = "exception_safety_guarantees.html#boost_optional.exception_safety_guarantees.swap" > Swap< / a >
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< / h4 >
< p >
< code class = "computeroutput" > < span class = "keyword" > void< / span > < span class = "identifier" > swap< / span > < span class = "special" > (< / span > < span class = "identifier" > optional< / span > < span class = "special" > < < / span > < span class = "identifier" > T< / span > < span class = "special" > > & ,< / span >
< span class = "identifier" > optional< / span > < span class = "special" > < < / span > < span class = "identifier" > T< / span > < span class = "special" > > & < / span > < span class = "special" > )< / span > < / code > has the same exception guarantee as < code class = "computeroutput" > < span class = "identifier" > swap< / span > < span class = "special" > (< / span > < span class = "identifier" > T< / span > < span class = "special" > & ,< / span > < span class = "identifier" > T< / span > < span class = "special" > & )< / span > < / code >
when both optionals are initialized. If only one of the optionals is initialized,
it gives the same < span class = "emphasis" > < em > basic< / em > < / span > exception guarantee as < code class = "computeroutput" > < span class = "identifier" > optional< / span > < span class = "special" > < < / span > < span class = "identifier" > T< / span > < span class = "special" > > ::< / span > < span class = "identifier" > reset< / span > < span class = "special" > (< / span > < span class = "identifier" > T< / span > < span class = "keyword" > const< / span > < span class = "special" > & < / span > < span class = "special" > )< / span > < / code > (since
< code class = "computeroutput" > < span class = "identifier" > optional< / span > < span class = "special" > < < / span > < span class = "identifier" > T< / span > < span class = "special" > > ::< / span > < span class = "identifier" > reset< / span > < span class = "special" > ()< / span > < / code > doesn't throw). If none of the optionals
is initialized, it has no-throw guarantee since it is a no-op.
< / p >
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< td align = "right" > < div class = "copyright-footer" > Copyright © 2003-2007 Fernando Luis Cacciola Carballal< 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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