[swift-evolution] Calling default implementation of protocols

[Jordan Rose]

I do think this would indeed be a feature worth having, but it would need design. There's also a simple workaround for now: put the default implementation in another method or a free function.

Jordan


> On Dec 8, 2015, at 9:43, Mateusz Zajac via swift-evolution <swift-evolution at swift.org> wrote:
> 
> If you define a simple protocol like:
> protocol Foo {
>     func testPrint()
> }
> And than you provide a default implementation for testPrint() method in protocol extensions like:
> extension Foo {
>     func testPrint() {
>         print("Protocol extension call")
>     }
> }
> You aren't allowed to call the fault implementation from the structure eg.
> struct Bar: Foo {
>     func testPrint() {
>         self.testPrint()
>         print("Call from struct")
>     }
> }
> This is some sort of limitation as often happens that a default implementation is providing a major part of implementation and only one, simple line is changed in actual struct implementation. If you're using classes you can achieve this by creating a base class and calling a method on super. If you consider structs, there's no such possibility and you always have to write a whole implementation from scratch in each structure which conforms to the protocol.
> You can use composition by creating nested structure, but it's neither logical nor clean... It's rather a hack...
> struct Bar: Foo {
>     func testPrint() {
>         // Calling default implementation
>         struct Dummy : Foo {}
>         let dummy = Dummy()
>         dummy.testPrint()
>         print("Call from struct")
>     }
> }
> 
> 
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