What does a retainCount represent in ARC?

Which one of the below functions definitions is wrong considering Swift language?

Which of these is a valid syntax for iterating through the keys and values of a dictionary? let dictionary = [keyOne : valueOne, keyTwo : valueTwo]

What is the name of the Swift language feature that Objective-C Blocks are translated into?

Which one creates a dictionary with a key type of Integer and value of String?

Which of these is an appropriate syntax for dispatching a heavy operation to a background thread?

What is the type of value1 in this code? let value1 = "\("test".count)"

The Codable protocol is _?

What is the correct way to call this function? func myFunc(_ a: Int, b: Int) -> Int {return a + b}

What is the type of this function? func add(a: Int, b: Int) -> Int { return a+b }

What is the value of y? var x: Int? let y = x ?? 5