Difference between String interpolation and String initializer in Swift

Question

I can read an int, float, double as a string using string interpolation or String initializer. result is always the same.

var a: Int = 2

var c: Character = "e"

var d: String = "\(a)\(c)"

OR

var d: String = String(a) + String(c)

the result is same. d has value "2e"

The only difference that I found is that string interpolation () can be used inside double quotes, whereas String() cannot be used inside double quotes.

Is that all? Am I missing something here?

Answer 1

String interpolation "\(item)" gives you the result of calling description on the item. String(item) calls a String initializer and returns a String value, which frequently is the same as the String you would get from string interpolation, but it is not guaranteed.

Consider the following contrived example:

class MyClass: CustomStringConvertible {
    var str: String

    var description: String { return "MyClass - \(str)" }

    init(str: String) {
        self.str = str
    }
}

extension String {
    init(_ myclass: MyClass) {
        self = myclass.str
    }
}

let mc = MyClass(str: "Hello")
String(mc)  // "Hello"
"\(mc)"     // "MyClass - Hello"