hashQuality.swift

// Test for uniqueness of hash values within a custom Hashable type
// Closer to 1.0 == fewer key collisions in a set or dictionary

extension Set {
  public var hashQuality: Double {
    let hashCount = Set<Int>(map({ $0.hashValue })).count
    return Double(hashCount) / Double(count)
  }
}

extension Dictionary {
  public var hashQuality: Double {
    let hashCount = Set(keys.map({ $0.hashValue })).count
    return Double(hashCount) / Double(count)
  }
}