[SR-7145] Dictionary.Values does not satisfy MutableCollection requirements #49693
Comments
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The least horrible solution seems to be that we keep Cocoa indices valid in the native dictionary. Cocoa-flavored Dictionary indices happen to contain a reference to their corresponding key, so we can extract that and look it up in the new instance. (We want to migrate to NSEnumerator-based indices soon, but we'll still have to keep the current key in the new index structure.) :-( |
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@swift-ci create |
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#19576 implements support for using indices belonging to bridged dictionaries to subscript native dictionaries that originated from the same NSDictionary instance (amongst other index validation improvements). #19694 enables native dictionaries to advance bridged indices. Unfortunately, Dictionary.Values is still not quite a MutableCollection, because there is no way I can see to support comparing bridged and native indices. (They define a completely different ordering.) |
Environment
Swift 4.1
Swift 4.2
Additional Detail from JIRA
md5: 4e2e499f88977c2bd588f64fee40342d
Issue Description:
For Dictionaries bridged over from Objective-C, Dictionary.Values does not correctly implement MutableCollection.
MutableCollection has the semantic requirement that the subscript setter must not invalidate indices. However, the Dictionary.Values.subscript setter converts to native storage, which invalidates existing (Cocoa) indices as a side effect:
import Foundation
let d = NSDictionary(dictionary: ["Hello": 1, "World": 2]) as Dictionary
let i = d.index(forKey: "Hello" as NSString)!
var values = d.values
values[i] = 42 as NSNumber
print(values[i]) // Traps, invalid index
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