we can make generate protocol like the follow:
protocol SomeDelegate {
typealias T
func xxx(x: T)
}
and make some class conform it:
class AA: SomeDelegate {
typealias T = Int
func xxx(x: T) {
// do some thing
}
}
and my problem was how to declare some propert conform to the generate protocol like this:
class BB {
var delegate: SomeDelegate
}
the code on above will raise error:
Protocol 'SomeDelegate' can only be used as a generic constraint
because it has Self or associated type requirements
It Seems I can use the protocol as delegate like follow:
class BB {
var delegate: AA?
}
but, this was not I want, it will cause my delegate can't inherit other parent class
Answers
You could use generics, using SomeDelegate as a type constraint:
class BB <U : SomeDelegate> {
var delegate: U? = nil
}
This way you'll only need to supply the type of U when you initialise an instance of BB:
struct MyStruct : SomeDelegate {
// The argument of xxx needs to be a concrete type here.
func xxx(x: Int) {
// ...
}
}
let bb = BB<MyStruct>()
Answers
There are few ways you can get through this error.
protocol SomeDelegate {
typealias T
func xxx(x: T)
}
Firstly use the proper type class for the function and the compiler infers the type itself.
class AA: SomeDelegate {
func xxx(x: Int) {
println(x)
}
}
Or, you can also override the typealias and assign it the proper type class like,
class AA: SomeDelegate {
typealias T = Int
func xxx(x: T) {
println(x)
}
}
And then use it just like the way you have done,
class B {
var someDelegate: AA?
}
