[stdlib] Dictionary.updateValue(_:,forKey:): Don’t overwrite the existing key #19592
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…ting key Replacing the old key with the new is unnecessary and somewhat surprising. It is also harmful to some usecases. rdar://problem/32144087 # Conflicts: # stdlib/public/core/NativeDictionary.swift
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@swift-ci please test |
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@swift-ci please test source compatibility |
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Merging. The source compat failure earlier evidently wasn't caused by this change. (It is also still occurring on master -- #19594.) |
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(This is the second attempt, after #19500 was reverted.)
updateValue(_:, forKey:)currently replaces the old key, which is undocumented, unnecessary and somewhat surprising. The previous incarnation of Dictionary implemented updates this way because of a technical detail; this wrinkle is now eliminated.rdar://problem/32144087
I know of no use cases where the old behavior was actually desirable; most/all practical code that would care about this seem to prefer to leave the old key in place.