toString and function issue

class Addresses {
    var streetname: String
    var streetnumber : Int
    var suburb: String
    var postcode:Int
    
    init( streetname:String, streetnumber:Int, suburb:String, postcode:Int ) {
        self.streetname = streetname
        self.streetnumber = streetnumber
        self.suburb = suburb
        self.postcode = postcode
    }
    func toString( streetname:String, streetnumber:Int, suburb:String, postcode:Int ) -> (String) {
        return (streetnumber),streetname, suburb, postcode
    }
}

I'm trying to create class named Address which stores the postcode, suburb, street name and street number of a building. An initialiser as well as a toString method which returns a String of a human-readable version of the class. This error message keeps popping up Cannot convert return expression of type 'Int' to return type 'String'