Use operator<=> instead of std::less for UniqueID.#183600
Use operator<=> instead of std::less for UniqueID.#183600auto-submit[bot] merged 2 commits intoflutter:masterfrom
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Internally when this is compiled with C++20, the compiler could not find the implementation for `std::less<UniqueID, UniqueID>`. Overridding `operator<` instead as that is the best practice in modern C++.
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This pull request updates the UniqueID struct to use operator< for comparison instead of a specialization of std::less. This is done by adding operator< to the UniqueID struct and removing the now-unnecessary std::less<impeller::UniqueID> specialization. This change aligns with modern C++ practices and resolves a compilation issue with C++20. I have one suggestion to improve the completeness of the UniqueID type by adding all relational operators.
| constexpr bool operator==(const UniqueID& other) const { | ||
| return id == other.id; | ||
| } | ||
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| constexpr bool operator<(const UniqueID& other) const { | ||
| return id < other.id; | ||
| } |
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For completeness and to fully adhere to the Google C++ Style Guide, it's good practice to define all relational operators if you define any. Since operator== and operator< are now defined, consider adding !=, >, <=, and >= as well.
If C++20 is available, you could use the spaceship operator operator<=> to have the compiler generate all of these for you. For example:
#include <compare>
// ...
auto operator<=>(const UniqueID&) const = default;If not, they can be implemented in terms of operator== and operator< as shown in the suggestion.
constexpr bool operator==(const UniqueID& other) const {
return id == other.id;
}
constexpr bool operator!=(const UniqueID& other) const {
return !(*this == other);
}
constexpr bool operator<(const UniqueID& other) const {
return id < other.id;
}
constexpr bool operator>(const UniqueID& other) const {
return other < *this;
}
constexpr bool operator<=(const UniqueID& other) const {
return !(other < *this);
}
constexpr bool operator>=(const UniqueID& other) const {
return !(*this < other);
}References
- The Google C++ Style Guide, which this repository follows, suggests that if you define any comparison operators, you should define all of them that are logical for the type. (link)
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The engine is now using C++20. So you can replace the std::less and operator== implementations for UniqueID with the default <=> operator.
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flutter/flutter@9e36adb...732e05d 2026-03-13 [email protected] Roll Dart SDK from 330b797abd09 to d5f6d3c17499 (1 revision) (flutter/flutter#183640) 2026-03-13 [email protected] Roll Skia from 9eb5598e1b2c to 029229d8be91 (3 revisions) (flutter/flutter#183638) 2026-03-13 [email protected] Roll Skia from 9be8fdf31ff4 to 9eb5598e1b2c (2 revisions) (flutter/flutter#183630) 2026-03-13 [email protected] Add awaits to flutter/test callsites (flutter/flutter#183487) 2026-03-13 [email protected] Add await to more flutter/flutter callsites (flutter/flutter#183413) 2026-03-13 [email protected] Roll Dart SDK from d1d84ab7ef0d to 330b797abd09 (2 revisions) (flutter/flutter#183624) 2026-03-13 [email protected] refactor: remove material import from sliver_resizing_header_test and sliver_prototype_item_extent_test (flutter/flutter#183562) 2026-03-13 [email protected] Fix reselection issue after the text is cleared (flutter/flutter#183545) 2026-03-13 [email protected] Roll Skia from 255bd243276b to 9be8fdf31ff4 (5 revisions) (flutter/flutter#183616) 2026-03-12 [email protected] ci: Remove `bringup` from orchestrator for windows_arm_host_engine on Linux (flutter/flutter#183574) 2026-03-12 [email protected] Use operator<=> instead of std::less for UniqueID. (flutter/flutter#183600) 2026-03-12 [email protected] Specified the repo the cp label will be removed from (flutter/flutter#183611) 2026-03-12 [email protected] [web] Fix Web SDK build on macOS (flutter/flutter#183549) 2026-03-12 [email protected] Roll Skia from 38761e1803d0 to 255bd243276b (3 revisions) (flutter/flutter#183603) 2026-03-12 [email protected] Roll Dart SDK from 2e1e7a09fce6 to d1d84ab7ef0d (1 revision) (flutter/flutter#183604) 2026-03-12 [email protected] Fix macOS relative plugin Xcode file path (flutter/flutter#183593) 2026-03-12 [email protected] Made cp labels get rejected on issues. (flutter/flutter#183595) 2026-03-12 [email protected] Roll Packages from ecace66 to 02f231f (4 revisions) (flutter/flutter#183594) 2026-03-12 [email protected] Roll Dart SDK from 59be21f25f2d to 2e1e7a09fce6 (1 revision) (flutter/flutter#183577) 2026-03-12 [email protected] Roll Skia from 46f41493ebf4 to 38761e1803d0 (6 revisions) (flutter/flutter#183590) If this roll has caused a breakage, revert this CL and stop the roller using the controls here: https://autoroll.skia.org/r/flutter-packages Please CC [email protected] on the revert to ensure that a human is aware of the problem. To file a bug in Packages: https://github.com/flutter/flutter/issues/new/choose To report a problem with the AutoRoller itself, please file a bug: https://issues.skia.org/issues/new?component=1389291&template=1850622 Documentation for the AutoRoller is here: https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md
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Internally when this is compiled with C++20, the compiler could not find the implementation for
std::less<UniqueID, UniqueID>. Overriddingoperator<=>instead as that is the best practice in modern C++.