How to have a singleton instance of a generic Class in Swift?

I have a singleton Class like this:

class Single {
    static let sharedInstance: Single = Single()
    ...
}

But I want to make the class generic like this:

class Single<T: Hashable> {
    static let sharedInstance: Single = Single()
    var dic: [T: Any] = [:] // Use the generic "T" here
}

I got this error from Xcode

Static stored properties not supported in generic types

I have searched Stackoverflow but none of the answers suit me.

For example, this one How to define static constant in a generic class in swift?

How can I solve this?

You can declare a generic type using a static computed property as follows:

class Single<T: Hashable> {
  static var sharedInstance: Single? {
    if self.sharedInstance != nil {
        return self.sharedInstance
    } else {
        return Single()
    }
  }
  var dic: [T: Any] = [:]
}