Class-only generic constraints in Swift

Question

I\'m trying to mark a variable of a generic type as weak:

class X {
  weak var t: T?
}

If I don\'t put in any constraints for

Answer 1

You want AnyObject, which the Swift docs describe as:

The protocol to which all classes implicitly conform.

class X<T: AnyObject> {
    weak var t: T?
}

class C { }
let x = X<C>()  // works fine
x.t = C()  

// error: type 'Int' does not conform to protocol ‘AnyObject’
// (because Int is a struct)
let y = X<Int>()