[clang-tools-extra] [clang-tidy] Adjust size-empty doc because C++11 size() is constant-time (PR #117629)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-tools-extra

Author: Niels Dekker (N-Dekker)

<details>
<summary>Changes</summary>

>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()`.

----

Notes:
- Microsoft's STL had implemented `empty()` as `return size() == 0`, until May 2021: https://github.com/microsoft/STL/pull/1836/files
- The time complexity of `size()` (specifically for `std::set`) was discussed by the library working group in 2007-2009: https://cplusplus.github.io/LWG/issue632

---
Full diff: https://github.com/llvm/llvm-project/pull/117629.diff


1 Files Affected:

- (modified) clang-tools-extra/clang-tidy/readability/ContainerSizeEmptyCheck.h (+4-6) 


``````````diff
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);

``````````

</details>


https://github.com/llvm/llvm-project/pull/117629