What's difference between "override public" and "public override"

Question

Diuming OP

Created Mar ’16

Replies 5

Boosts 0

Views 3.6k

Participants 4

What's difference between "override public" and "public override" for access control in swift

public class MyPopUpButton: NSPopUpButton {
  
     // way 1
     override public func mouseDown(theEvent: NSEvent) {
     }

     // way 2
     public override func mouseDown(theEvent: NSEvent) {
     }
}

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Answer 1

RLKingSoftware OP

Mar ’16

In the first, you're overriding a public func. In the second, you're making public the

fact that you're overriding the func.

Put another way, you're making mouseDown public in the first example. In the

second, your making your override public but not mouseDown.

0

Answer 2

QuinceyMorris OP

Mar ’16

Er, I'm pretty sure there's no difference whatsoever. If there was, you could leave out "public" in one or other of the cases, but in fact you can't.

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Answer 3

RLKingSoftware OP

Mar ’16

The order does effect how the compiler treats things. If it didn't, there would be no point

in the public keyword even existing.

0

Answer 4

QuinceyMorris OP

Mar ’16

Look at the grammar:

https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/declaration-modifiers

There's clearly no particular order to "declaration modifiers", and "override" and "public" are both declaration modifiers.

You can try this in a playground:

public class A {
  public func a () {}
}

public class B: A {
  override func a () {}
}

You get an error "Overriding instance instance method must be at least as accessible as the declaration it overrides". You can insert "public" before or after "override" to fix this.

If you claim a difference between the two forms, can you give an example where something using the subclass can tell the difference?

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Answer 5

honkmaster OP

Mar ’16

No difference.

0