Convenience.swift

struct DataStructure {
    var x: Int
    var s: String
}



// Create a "convenience" namespace to separate properties and functions which we
// don't want confused with being actual properties of the original structure.
extension DataStructure {
    var convenience: Convenience {
        return Convenience(data: self)
    }
    
    struct Convenience {
        let data: DataStructure
        
        var description: String {
            return "\(data.x) \(data.s)"
        }
      
        // ...
    }
}



var ds = DataStructure(x: 5, s: "Hello")
print(ds.convenience.description)
ds.x = 9
print(ds.convenience.description)