can swift functions and closures conform to Hashable?

Question

Suppose I want to have a Set of functions or closures. Here's how I would go about it:

typealias HandlerX = () -> ()
static var handlersX = Set<HandlerX>()

This produces the following compiler error:

Type 'HandlerX' (aka '() -> ()') does not conform to protocol 'Hashable'

Is this a dead end?

Answer 1

Yes, this is a dead end. Hashable isn't really your problem; there's no way to decide whether two closures are Equal (which is a base requirement of Hashable).

Answer 2

You can create a wrapper struct for closure

struct Hashed<T>: Hashable {

  let value: T
  let hash: Int

  init(value: T, hash: Int) {
    self.value = value
    self.hash = hash
  }

  public func hash(into hasher: inout Hasher) {
    hasher.combine(hash)
  }

  static func == (lhs: Hashed<T>, rhs: Hashed<T>) -> Bool {
      lhs.hashValue == rhs.hashValue
  }
}

But you need to understand the identity of your closures. For example, it can be the class that created it, or #filename + #line , or always unique with UUID()