How to avoid using value capture when C++ uses variables non-locally

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If you capture variables that can be used non-locally, you should avoid using referenced snaps in lambda expressions. Non-local uses include returning, saving in the heap, or passing to other threads.

Reason (reason)

Pointers and references to local variables should not have a lifetime longer than their scope. A lambda expression that captures a variable by reference is just another place to hold a reference to a local variable, and variable capture in the form of a reference should not be used if the lifetime of the lambda expression (or copy) exceeds scope.

Example, bad (negative example)

Int local = 42

/ / Want a reference to local.// Note, that after program exits this scope,// local no longer exists, therefore// process () call will have undefined qualified thread pool.queueworkwork{ process (local);})

Example, goodint local = 42 Want a copy of local.// Since a copy of local is made / Want a copy of local.// Since a copy of local is made, it will// always be available for the call.thread_pool.queue_work ([=] {process (local);})

Enforcement

(Simple) Warn when capture-list contains a reference to a locally declared variable

(simple) alarm when the capture list contains locally declared variables.

(Complex) 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

(complex) prompt when a variable pointing to a local declaration is included in the capture list and the lambda expression is passed to a non-constant or non-local context.

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