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F.53: More comprehensive example and enforcements.

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psliwa 2016-02-03 18:27:31 +01:00
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@ -3149,18 +3149,27 @@ This is a simple three-stage parallel pipeline. Each `stage` object encapsulates
Pointers and references to locals shouldn't outlive their scope. Lambdas that capture by reference are just another place to store a reference to a local object, and shouldn't do so if they (or a copy) outlive the scope. Pointers and references to locals shouldn't outlive their scope. Lambdas that capture by reference are just another place to store a reference to a local object, and shouldn't do so if they (or a copy) outlive the scope.
##### Example ##### Example, bad
{ {
// ... int local_variable = 42;
background_thread.queue_work([&]{ process(local_variable); }); // Want a reference to local_variable.
// Note, that after program exists this scope, local_variable does no longer exist,
// therefore process() call will have undefined behavior!
}
// a, b, c are local variables ##### Example, good
background_thread.queue_work([=]{ process(a, b, c); }); // want copies of a, b, and c
{
int local_variable = 42;
background_thread.queue_work([=]{ process(local_variable); }); // Want a copy of local_variable.
// Since a copy of local_variable is made, it will be available at all times for the call.
} }
##### Enforcement ##### Enforcement
??? * **Easy:** Warn, when capture-list contains a reference to a locally declared variable
* **Medium:** Flag, when capture-list contains a reference to a locally declared variable and the lambda is passed to a non-`const` and non-local context
### <a name="Rf-this-capture"></a>F.54: If you capture `this`, capture all variables explicitly (no default capture) ### <a name="Rf-this-capture"></a>F.54: If you capture `this`, capture all variables explicitly (no default capture)