What criteria must be met for successful addition of an element to a Dictionary collection?

To successfully add an element to a Dictionary collection in Swift, the following criteria must be met:

• The key must be unique in the dictionary. If the key already exists, the value for that key will be updated.
• The key must conform to the Hashable protocol so that the dictionary can compute the hash and quickly find the element.
• The value can be of any type, but must conform to the declared type of the dictionary.

Example of adding an element:

var dict = [String: Int]()
dict["apple"] = 5  // adding a key-value pair