Cannot override more than one superclass declaration

Using Swift
1

Hi there,

I came across an issue I've never had before, and am curious if there's a workaround, or this is an expected behavior / a known limitation of current version's.

class Foo {
  func a<T>(_ val: T) -> String { return "not equatable" }
  func a<T: Equatable>(_ val: T) -> String { return "equatable" }
}

class Bar: Foo {
  // these work like a charm
  func b<T>(_ val: T) -> String { return super.a(val) }
  func b<T: Equatable>(_ val: T) -> String { return super.a(val) }

  // "declaration 'a' cannot override more than one superclass declaration"
  override func a<T>(_ val: T) -> String { return super.a(val) }
  override func a<T: Equatable>(_ val: T) -> String { return super.a(val) }
}

let bar = Bar()
bar.b(1)  // "equatable"
bar.b(Int.self)  // "not equatable"

While I can call two superclass methods individually, why can't I override them separately?

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2

Definitely seems like a bug! Please file at https://bugs.swift.org.

(I see why it's trying to do this: the <T> version of a is general enough to handle the whole <T: Equatable> version as well as the one it's actually trying to override. But when there's an exact match like this it shouldn't be considered a problem.)

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3

Filed - [SR-10198] Cannot override more than one superclass declaration · Issue #52598 · apple/swift · GitHub

2 Likes