[swift-evolution] [Accepted] SE-0156: Class and Subtype existentials

[Karl Wagner]

Do we support where clauses on these existentials? For example, can I write:    
  
  
  

  
func doSomething<T>(_: NSObject  &  Collection where Iterator.Element == T)
  

  
The proposal says nothing about where clauses.
  

  
- Karl
  
  

  
  
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> On Mar 20, 2017 at 7:00 pm,  <Douglas Gregor via swift-evolution (mailto:swift-evolution at swift.org)>  wrote:
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> Proposal link:
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> > https://github.com/apple/swift-evolution/blob/master/proposals/0156-subclass-existentials.md
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> Hello Swift community,
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> The review of SE-0156 “Class and Subtype Existentials” ran from February 28...March 7, 2017. The proposal was very well-received and is  accepted  with one modification: the ordering rules for existential types that involve AnyObject or a class type will be removed.
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> The ordering rules were intended to improve code clarity by requiring that the class (or AnyObject) constraint come first—“AnyObject  &  P” would be well-formed but   “P  &  AnyObject” would be an error—enforcing more uniformity for Swift code and echoing a similar restriction that already exists for class definitions, where the superclass must come first. However, the ability to compose typealiases complicated the   ordering rules   considerably, and—as noted by Matthew Johnson (https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20170227/033365.html)—don’t provide the guarantee that the class constraint will always be first. Therefore, the core team felt that the resulting ordering rules   introduced more complexity than they provided clarity, and therefore do not belong in the language.   
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> Thanks,
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> Doug Gregor, Review Manager
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>  _______________________________________________ swift-evolution mailing list swift-evolution at swift.org https://lists.swift.org/mailman/listinfo/swift-evolution        
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