22b4470f2a
Update all links to C++ Core Guidelines to `e49158a`.
Refresh done using the following script and some manual edits:
db76e34e74/personal/fred-tingaud/rspec/refresh-cppcoreguidelines.py
When re-using this script, be mindful that:
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Co-authored-by: Marco Borgeaud <marco.borgeaud@sonarsource.com>
58 lines
1.7 KiB
Plaintext
58 lines
1.7 KiB
Plaintext
== Why is this an issue?
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If the lifetime of the arguments passed to a lambda function is longer than the lifetime of the lambda itself, these arguments can be passed by reference.
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Doing so avoids copying potentially big objects and it should be preferred over using copy capture.
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This rule reports an issue if a lambda passed into an algorithm that uses it locally (all algorithms in headers ``++<algorithm>++`` and ``++<numeric>++``) captures some values.
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=== Noncompliant code example
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[source,cpp]
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----
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using Vec = vector<int>;
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Vec applyPermutation(const Vec& v, const Vec& permutation) {
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assert(v.size() == permutation.size());
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const auto n = v.size();
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Vec result(n);
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// Noncompliant: this will copy the entire v vector for each iteration, resulting in n^2 operations
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transform(permutation.begin(), permutation.end(), back_inserter(result),
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[v](int position){ return v[position]; });
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return result;
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}
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----
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=== Compliant solution
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[source,cpp]
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----
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using Vec = vector<int>;
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Vec applyPermutation(const Vec& v, const Vec& permutation) {
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assert(v.size() == permutation.size());
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const auto n = v.size();
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Vec result(n);
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// Compliant: this will NOT copy the entire v vector for each iteration, resulting in n operations
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transform(permutation.begin(), permutation.end(), back_inserter(result),
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[&v](int position){ return v[position]; });
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return result;
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}
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----
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== Resources
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* {cpp} Core Guidelines - https://github.com/isocpp/CppCoreGuidelines/blob/e49158a/CppCoreGuidelines.md#f52-prefer-capturing-by-reference-in-lambdas-that-will-be-used-locally-including-passed-to-algorithms[F.52: Prefer capturing by reference in lambdas that will be used locally, including passed to algorithms]
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