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[SR-2801] Need a way to implement Sequence from Obj-C code. #45405

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swift-ci opened this issue Sep 29, 2016 · 3 comments
Open

[SR-2801] Need a way to implement Sequence from Obj-C code. #45405

swift-ci opened this issue Sep 29, 2016 · 3 comments
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improvement standard library Area: Standard library umbrella

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@swift-ci
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Previous ID SR-2801
Radar None
Original Reporter mikelehen (JIRA User)
Type Improvement
Additional Detail from JIRA
Votes 0
Component/s Standard Library
Labels Improvement
Assignee None
Priority Medium

md5: 9396e06997f092bc2380dacf6f4911a9

Issue Description:

See http://stackoverflow.com/questions/39757563/how-do-i-implement-sequence-to-allow-swifts-for-in-syntax-from-objective-c for details.

But basically, it doesn't seem as there's any way to write a StringList class in Obj-C that can be iterated in swift with for-in syntax:

let list = StringList()
for y: String in list {
  ...
}

It seems if I derive from NSEnumerator<NSString *>, then for-in works except the generic type is lost, and so declaring y as String gives a "'NSFastEnumerationIterator.Element' (aka 'Any') is not convertible to 'String'" error.
@belkadan
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@dabrahams, did we ever figure out if it was a good idea to use NSFastEnumeration to implement Sequence?

@belkadan
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I guess the importer can't do it automatically, but we could derive Sequence from NSFastEnumeration instead of making people write the makeIterator call with NSFastEnumerationIterator explicitly.

@swift-ci
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Comment by Michael Lehenbauer (JIRA)

Any chance the generic type could also be preserved somehow? I'd like my for-in to work without having to as! cast from Any to String...

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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improvement standard library Area: Standard library umbrella
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@belkadan @swift-ci