协议的指定初始化程序类

Question

I'd like to use a protocol name as an initializer. Something like this:

protocol Foo { ... }
protocol Bar : Foo { ... }

class FooImpl : Foo { ... }

where let foo = Foo() will defer to FooImpl() when assigning to foo . Is there a way to specify a 'designated initializer class' for a protocol?

Another option might be:

class Foo {
  class FooImpl { ... }
  init () {
    // somehow create a FooImpl
  }
}

Is the above possible? But, not sure this second case is practical given that properties can't be declared in Foo unless they are implemented therein.

Answer 1

I'd use the factory pattern here:

class FooFactory {
  class func createFoo -> Foo {
    return FooImpl()
  }
}

...

let foo = FooFactory.createFoo()