I'm trying to play around a bit with Swift, protocols and protocol extensions. Specifically I'm trying to provide a default implementation of a protocol in a protocol extension. This is my code:
protocol Proto : class {
func someMethod() -> String
}
extension Proto {
static func create() -> Self {
return ProtoDefaultImpl() as! Self
}
}
class ProtoDefaultImpl : Proto {
func someMethod() -> String {
return "doing something"
}
}
let instance = Proto.create()
let output = instance.someMethod()
print(output)
The compiler complains on the line where I call Proto.create(), with the following error: error: static member 'create' cannot be used on instance of type 'Proto.Protocol'.
Have I missed something here? Is there any way you can achieve this?
Thanks.
You can't call the method on the protocol itself, you have to call it on a type that implements the protocol. This doesn't change because there is a default implementation of the protocol in an extension. Change your type from Proto to ProtoDefaultImpl and it will work as you expect.
protocol Proto : class {
func someMethod() -> String
}
extension Proto {
static func create() -> Self {
return ProtoDefaultImpl() as! Self
}
}
class ProtoDefaultImpl : Proto {
func someMethod() -> String {
return "doing something"
}
}
let instance = ProtoDefaultImpl.create()
let output = instance.someMethod()
print(output)
This outputs: doing something
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