~= operator in Swift

Question

I recently downloaded the Advanced NSOperations sample app from Apple and found this code...

// Operators to use in the switch statement.
pr         


        

Answer 1

It is an operator used for pattern matching in a case statement.

You can take a look here to know how you can use and leverage it providing your own implementation:

• http://oleb.net/blog/2015/09/swift-pattern-matching/
• http://austinzheng.com/2014/12/17/custom-pattern-matching/

Here is a simple example of defining a custom one and using it:

struct Person {
    let name : String
}

// Function that should return true if value matches against pattern
func ~=(pattern: String, value: Person) -> Bool {
    return value.name == pattern
}

let p = Person(name: "Alessandro")

switch p {
// This will call our custom ~= implementation, all done through type inference
case "Alessandro":
    print("Hey it's me!")
default:
    print("Not me")
}
// Output: "Hey it's me!"

if case "Alessandro" = p {
    print("It's still me!")
}
// Output: "It's still me!"