Swift StringLiteralConvertible

StringLiteralConvertibleExample

public class Foo : StringLiteralConvertible {
    
    var num:Int = 0

    required public init(stringLiteral value: StringLiteralType) {
        self.num = value.toInt()!
        // of course you can do something more complicated by parsing the value.
    }
    
    public typealias UnicodeScalarLiteralType = StringLiteralType
    convenience required public init(unicodeScalarLiteral value: UnicodeScalarLiteralType) {
        self.init(stringLiteral: value)
    }
    
    public typealias ExtendedGraphemeClusterLiteralType = StringLiteralType
    required convenience public init(extendedGraphemeClusterLiteral value: ExtendedGraphemeClusterLiteralType) {
        self.init(stringLiteral: value)
    }
}

var foo:Foo = "1"

StringLiteralConvertible conforms to protocol ExtendedGraphemeClusterLiteralConvertible which in turn conforms to UnicodeScalarLiteralConvertible. That is why you need three inits.