Context

I am currently working with Protocols and encountered a problem. My Protocol has a Static Type and I would like to access it from an Instance of a Struct conforming to this Protocol. However, this results in the following Compiler Error:

Compiler Error: Value of type 'any Component' has no member 'Self'

Code

protocol Component {
    static var name: String { get set }
}

struct ComponentA: Component { static var name: String = "Component A" }
struct ComponentB: Component { static var name: String = "Component B" }

struct MainView: View {
    var body: some View {
        Text(component.Self.name) // Compiler Error (see Context)
    }

    private var component: any Component {
        // Returns any component (ComponentA or ComponentB).
    }
}

Question

How can I access the Type of the Instance conforming to the Protocol, e.g. ComponentA or ComponentB with the Self Syntax?

Note: I also tried type(of: component).name which works. However, I am wondering why the Self Syntax is giving me a Compiler Error.

CodePudding user response：

The reason why component.Self doesn't work is because Self is a type, and you are using it like a member of component. component.Self doesn't make sense for the same reason that 1.Int, or "foo".String doesn't make sense. component doesn't have a member called Self.

You can, however, add a member called Self to Component using an extension:

extension Component {
    var Self: Self.Type { type(of: self) }
}

Now your component.Self.name would work.

But I don't quite see much point in doing this, when just writing type(of: component).name works as well.

Side note: unlike component.Self that doesn't make sense, type(of: component) is an expression (a function call to be specific) of type any Component.Type. This is what allows you to access name, because any Component.Type does have a member called name.

See also: Self Types in the Swift Language Reference