Halfway last month, Erica Sadun wrote a blog entry where she used the reflect() function: Swift: Just because
She just gave the code and didn't comment any further so below, I've liberally sprinkled the code with comments:
// Define a struct to represent a point
struct Pt {
let x: Int
let y: Int
init(_ x: Int, _ y: Int) {self.x = x; self.y = y}
init(){self.init(0, 0)}
}// Declare an instance of Pt let p = Pt(2, 3)
// Any means: any reference (i.e. class) or value type (i.e. struct, number, etc)
// So this function will take an item that can be basically anything in Swift
// and look through the names of its members to see if the string matches.
func valueForKey(item : Any, key: String) -> Any? { // The built-in Swift reflect() function is used by Xcode to aid in debugging
let mirror = reflect(item)
// It returns an array, walk through it
for index in 0..<mirror.count {
// Each item in the array has a member called 0 and 1
// This assignment is only there for readability's sake
let child = mirror[index]
// The .0 member is a string and it holds the name of our struct member
if key == child.0 {
// The .1 member holds information about our struct member
// If it's not an optional, return its value with the .value property
return child.1.value
}
}
return nil
}// Try it out valueForKey(p, "x")
Instead of using the valueForKey() function, you can also open a Playground and try out a few things yourself:
let mirror = reflect(p) println(mirror[0]) println(mirror[0].0) println(mirror[0].1) println(mirror[0].1.value)
