From 4fc0beafc385c3f326b47dbdfaf356ccc1e1200c Mon Sep 17 00:00:00 2001 From: psliwa Date: Wed, 3 Feb 2016 18:27:31 +0100 Subject: [PATCH] F.53: More comprehensive example and enforcements. --- CppCoreGuidelines.md | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-) diff --git a/CppCoreGuidelines.md b/CppCoreGuidelines.md index 33c39ae..925de0e 100644 --- a/CppCoreGuidelines.md +++ b/CppCoreGuidelines.md @@ -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. -##### 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 - background_thread.queue_work([=]{ process(a, b, c); }); // want copies of a, b, and c +##### Example, good + + { + 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 -??? +* **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 ### F.54: If you capture `this`, capture all variables explicitly (no default capture)