[swift-users] How to call a private protocol extension method from a public protocol extension method

[Kevin Greene]

You could have your common superclass implement your protocol. E.g...

public protocol PublicProto {

  func publicFn()

}


public class CommonSuper: PublicProto {

  public func publicFn() { specificPrivate() }

  private func specificPrivate() {}

}


private class SubA: CommonSuper {

  override private func specificPrivate() { /* ... */ }

}


private class SubB: CommonSuper {

  override  private func specificPrivate() { /* ... */ }

}

I don't know what you're doing specifically, but I would guess that a
cleaner approach would likely be to get rid of the super class entirely,
and pull the shared logic from your two subclasses into a separate object
that both classes instantiate, or have injected. Then have your two classes
implement PublicProto directly. That discussion would probably be best had
on another mailing list though.

On Wed, Jun 22, 2016 at 11:19 AM, David Ungar via swift-users <
swift-users at swift.org> wrote:

> I love protocol-oriented programming because of the guarantees that come
> with value types. But I cannot figure out how to do the same factoring I
> can do with the class side of the the language. I want to factor out common
> code into a public method that calls specific code in a private method & I
> want to do this for value types.
>
> Here it is in classes:
>
> public class CommonSuper {
>   public func publicFn() { … specificPrivateFn()  … }
>   private func specificPrivateFn() { }
> }
>
> private class SubA {
>   override private func specificPrivate() { … }
> }
> private class SubB {
>   override  private func specificPrivate() { … }
> }
>
> I have tried it lots of ways with protocols, and can get none to compile.
> Here is one:
>
> public protocol PublicProto {
>     func publicFn()
> }
>
> private protocol PrivateProto {
>     func specificPrivateFn()
> }
>
> public extension  PublicProto where Self: PrivateProto { // Error:
> Extension cannot be declared public because its generic requirement uses a
> private type
>     public func publicFn() { specificPrivateFn() } // Error: Cannot
> declare a public instance method in an extension with private requirements
> }
>
> private struct SA: PublicProto, PrivateProto {
>     private func specificPrivateFn() {}
> }
> private struct SB: PublicProto, PrivateProto {
>     private func specificPrivateFn() {}
> }
>
> What am I doing wrong?
>
> Thanks,
>
> - David
>
> _______________________________________________
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> swift-users at swift.org
> https://lists.swift.org/mailman/listinfo/swift-users
>
>
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