Check if key exists in dictionary of type [Type:Type?]

Question

How can I check if a key exists in a dictionary? My dictionary is of type [Type:Type?].

I can\'t simply check dictionary[key] == nil, as th

Answer 1

I handled it this way in Swift 4:

extension Dictionary {
    func contains(key: Key) -> Bool {
        let value = self.contains { (k,_) -> Bool in key == k }
        return value
    }
}

This uses Dictionary.contains(where: (key: Hashable, value: Value) throws -> Bool). By encapsulating it as an extension I have a good shot at updating the implementation to something better without modifying my code. I'm avoiding creating data, which index(forKey:Key) does. I'm hoping it's more efficient than accessing keys since that must create the whole array before searching it.