[clang-tidy] Adjust size-empty doc because C++11 size() is constant-time #117629
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@llvm/pr-subscribers-clang-tidy @llvm/pr-subscribers-clang-tools-extra Author: Niels Dekker (N-Dekker) ChangesFrom C++11, a conforming Notes:
Full diff: https://github.com/llvm/llvm-project/pull/117629.diff 1 Files Affected:
diff --git a/clang-tools-extra/clang-tidy/readability/ContainerSizeEmptyCheck.h b/clang-tools-extra/clang-tidy/readability/ContainerSizeEmptyCheck.h
index 617dadce76bd3e..acd8a6bfc50f5e 100644
--- a/clang-tools-extra/clang-tidy/readability/ContainerSizeEmptyCheck.h
+++ b/clang-tools-extra/clang-tidy/readability/ContainerSizeEmptyCheck.h
@@ -18,12 +18,10 @@ namespace clang::tidy::readability {
/// a call to `empty()`.
///
/// The emptiness of a container should be checked using the `empty()` method
-/// instead of the `size()` method. It is not guaranteed that `size()` is a
-/// constant-time function, and it is generally more efficient and also shows
-/// clearer intent to use `empty()`. Furthermore some containers may implement
-/// the `empty()` method but not implement the `size()` method. Using `empty()`
-/// whenever possible makes it easier to switch to another container in the
-/// future.
+/// instead of the `size()` method. It shows clearer intent to use `empty()`.
+/// Furthermore some containers may implement the `empty()` method but not
+/// implement the `size()` method. Using `empty()` whenever possible makes it
+/// easier to switch to another container in the future.
class ContainerSizeEmptyCheck : public ClangTidyCheck {
public:
ContainerSizeEmptyCheck(StringRef Name, ClangTidyContext *Context);
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dzenanz
approved these changes
Nov 25, 2024
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A personal note: yes, I like clang-tidy's readibility-container-size-empty check, I think it's great! And I do very much prefer |
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You understand that this check does not apply only to std:: containers but also to boost and other custom one that have size and empty methods. In such case claim is still valid. If you change check description, then check documentation also should be updated to be in sync. |
Thanks for your prompt reply, Piotr. I thought of custom containers too, but then again, I would rather not make any claim about the efficiency of In order for the documentation to make claims about But then, do you happen to know whether there are indeed still Boost containers that have a
Thanks! So this pull request should make some more adjustments before it can be merged (if it would be accepted at all)? |
HerrCai0907
reviewed
Nov 26, 2024
I think we should remove the discussion about efficient in claim since it is misleading after C++11. For self-defined container, because implement of empty and size can be totally different, this claim is still misleading. |
From C++11, a conforming `size()` method is guaranteed to be a constant-time function. `empty()` is not _generally_ more efficient than `size()`. It might even be implemented in terms of `size()`.
N-Dekker
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clang-tidy-ContainerSizeEmptyCheck-constant-time-size
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Thanks for your encouragement, @HerrCai0907. I just force-pushed, as you suggested. To further clarify my motivation, I believe that C++ users actually got the impression from the documentation that this check will make their code faster. ITK pull request InsightSoftwareConsortium/ITK#4985 ("PERF: readability container size empty") was also labeled as a performance improvement, while I think it is very unlikely to have any effect on the run-time performance. |
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@PiotrZSL @HerrCai0907 Thank you both for your feedback and approval! Would one of you be able the merge the pull request? |
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/17/builds/4311 Here is the relevant piece of the build log for the reference |
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From C++11, a conforming
size()method is guaranteed to be a constant-time function.empty()is not generally more efficient thansize(). It might even be implemented in terms ofsize().Notes:
empty()asreturn size() == 0, until May 2021: https://github.com/microsoft/STL/pull/1836/filessize()(specifically forstd::set) was discussed by the library working group in 2007-2009: https://cplusplus.github.io/LWG/issue632