Swift protocol for string interpolation

Question

What protocol do I have to implement to control the way an object is represented within a string interpolation in Swift?

I wan\'t to specify what get\'s printed in somet

Answer 1

In Swift 5 Apple introduced Custom String Interpolation.

Suppose you have person struct with two properties name and age.

struct Person {
  var name: String
  var age: Int
} 

If you wanted to add a special string interpolation for that so that we can print persons in descriptive way, we can add an extension to String.StringInterpolation with a new appendInterpolation() method.

 extension String.StringInterpolation {
       mutating func appendInterpolation(_ person: Person) {
       appendInterpolation("My name is \(person.name) and I'm \(person.age) years old.")
    }
}

Now If we print the person details like:

 let person = Person(name: "Yogendra", age: 28)
 print("Person Details: \(person)")

Output will be:

Person Details: My name is Yogendra and I'm 28 years old.