If you have been programming for a few years, you have undoubtedly come across the term Reflection. This feature allows us to inspect and work with the members of a type.

if this doesn’t make sense, suppose you wanted to check what members a type has. How would you do this? Ideally you’d like to iterate over its members and print them. This is a very basic application of Reflection, but it should let think of other potential uses for it.

Introducing Mirror

Mirror is an object that allows us to inspect the members of a type - it can be class, struct, or even a protocol. It’s simplest use doesn’t give much of a challenge.

You start by creating your object:

struct Person {
  let name: String
  let age: Int
}

Then create an object, and reflect it:

let andy = Person(name: "Andy Ibanez", age: 28)

let andyMirror = Mirror(reflecting: andy)

andyMirror.children.forEach {
  print("Member: \($0.label)")
  print("Value: \($0.value)")
}

The above code would print:

Member: Optional("name")
Value: Andy Ibanez
Member: Optional("age")
Value: 28

We iterate over each property, and print its value.

Conclusion

Reflection is a very interesting feature that allows to create some sort of meta-programming in Swift. While not applicable to many use cases, it’s important to be aware of its existence.