Fogmeister Fogmeister - 1 year ago 79
Swift Question

~= operator in Swift

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

// Operators to use in the switch statement.
private func ~=(lhs: (String, Int, String?), rhs: (String, Int, String?)) -> Bool {
return lhs.0 ~= rhs.0 && lhs.1 ~= rhs.1 && lhs.2 == rhs.2

private func ~=(lhs: (String, OperationErrorCode, String), rhs: (String, Int, String?)) -> Bool {
return lhs.0 ~= rhs.0 && lhs.1.rawValue ~= rhs.1 && lhs.2 == rhs.2

It seems to use the
operator against
but I've never seen it before.

What is it?

Answer Source

It is an operator used for pattern matching inside the switch statement.

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

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 == 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!")
    print("Not me")

// Output: "Hey it's me!"