Reflection in Swift

Or are we talking introspection?

Steven Curtis
3 min readSep 16, 2019


Does this represent Reflection, or Introspection??

It is often claimed that reflection is not really used in Swift as it is a statically typed language, but actually it gives us read-only access to an object’s properties (importantly) at runtime.

If you have a class you can use reflection to iterate through all of the values

Difficulty: Easy | Normal | Challenging


  • Be able to (at least) create a “Hello, World!” App in Playgrounds (guide HERE)
  • Swift data types, some understanding of OO concepts.


Any: An instance of any type, including function types

Introspection: A way to look at an object’s properties without modifying them. Swift reflection should rather be called introspection.

Mirror: A description of the parts that make up a particular instance. For Swift, access to these objects is read-only.

Reflection: An API used to examine or modify the behaviour of methods, classes and interfaces at runtime.

Uses of mirror in Swift

Inspect type data of structs or classes

Basically we can query data in our code. That means we can read through the list of properties that are available at runtime. Here we

enum Species {
case dog
case cat
struct Animal {
var name: String
var species: Species
var taylor = Animal(name: "Derek", species: .dog)
var mirror = Mirror(reflecting: taylor)
print (mirror) // "Mirror for Animal"

The printing here that prints to the console “Mirror for Animal” is not too interesting. The result that you should be looking for is to iterate through the mirror to print out the properties of the Animal struct.

for case let (label?, value) in mirror.children {
print (label, value) // "name Derek", "species dog"

Iterate over tuples inspecting elements using Mirror