Generating unique ids for each implementor of a protocol-CodePudding

I have the following I want to achieve in Swift:

I have a protocol

protocol IdProtocol {
  static var id: Int { get }
}

Now I want each implementor of this potocol to have a different value for id.

For example:

struct One: IdProtocol {}
struct Two: IdProtocol {}

Here, One will have id 0 and Two will have id 1 (or vice versa).

How can I implement this in Swift? I'd like to have this as a protocol extension so that all structs implementing IdProtocol will automatically be assigned an id. This can be done lazily.

I haven't been able to find a solution to this.

CodePudding user response：

You won't be able to create it in this way that there is a consecutive Int, starting at 0 and incrementing for each type automatically. You would have to solve all kinds of issues in a manual way.

Which is the implementation where the counter starts?
What is the counter when the compiler encounters the next implementation?
What happens if the compile order changes? Is this critical if the ids change each time you compile?

What you could do however is the following: use a protocol extension to define a standard implementation for id and hash the name of the type:

extension IdProtocol {
    static var id: Int {
        var hasher = Hasher()
        hasher.combine(String(describing: Self.self))
        return hasher.finalize()
    }
}

This should be enough for most cases. But it will be a (more or less) random Int for each type. Still, that id will stay constant between compiler runs (until you rename a class). And you should only run into collisions when the names collide as well.