Fix chain potentially mutating a stale object #10643
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The constructor of the result of std.range.chain copies it's input tuple and then has to check which of the input-ranges in the first non-empty one. The member function empty is not guaranteed to be const, filter is probably the most prominent function that has to be "primed". On the first call to empty(), filter will try to advance all it's input ranges to the first element that matches the predicate. For ranges with full value semantics, using the old input object instead of the new internal buffer means that the work of priming is done twice. If any ranges have reference semantics, the references gets advances, but the value-semantic parts of the range-composition gets reset. This fixes dlang#10561 and dlang#9877
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Thanks for your pull request and interest in making D better, @Inkrementator! We are looking forward to reviewing it, and you should be hearing from a maintainer soon.
Please see CONTRIBUTING.md for more information. If you have addressed all reviews or aren't sure how to proceed, don't hesitate to ping us with a simple comment. Bugzilla referencesYour PR doesn't reference any Bugzilla issue. If your PR contains non-trivial changes, please reference a Bugzilla issue or create a manual changelog. Testing this PR locallyIf you don't have a local development environment setup, you can use Digger to test this PR: dub run digger -- build "master + phobos#10643" |
thewilsonator
approved these changes
Feb 19, 2025
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The constructor of the result of std.range.chain copies it's input tuple and then has to check which of the input-ranges in the first non-empty one. The member function empty is not guaranteed to be const, filter is probably the most prominent function that has to be "primed". On the first call to empty(), filter will try to advance all it's input ranges to the first element that matches the predicate.
For ranges with full value semantics, using the old input object instead of the new internal buffer means that the work of priming is done twice. If any ranges have reference semantics, the references gets advances, but the value-semantic parts of the range-composition gets reset.
This fixes #10561 and #9877