In our first chapter on Property wrappers we saw some SwiftUI native examples that not only allow you to encapsulate functionality that's commonly associated with properties, like @State, but they also allow you to add custom behaviors to properties without duplicating code.
Today we are going to explore how to write our custom Property wrappers to improve readability and maintainability.
Defining A Property Wrapper
@propertyWrapper attribute and can apply it to properties in a class, struct, or enum. The core requirement for a property wrapper is a wrappedValue property that provides the underlying value.
Let's start with a basic example: a property wrapper that logs changes to a property whenever its value is modified.
@propertyWrapper
struct Validator { // 1
private var value: String
init(wrappedValue: String) { // 2
self.value = wrappedValue
}
var wrappedValue: String {
get { value }
set {
print("Email changed from \"\(value)\" to \"\(newValue)\"") // 3
value = newValue
}
}
}
struct User { // 4
@Validator var email: String
}
var user = User(email: "test")
user.email = "test@educaswift.com"
// Prints: Value changed from "test" to "test@educaswift.com"
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