Basic Guide to Property Wrapper with Swift. Read more at https://fxstudio.dev/property-wrapper-trong-10-phut/

PropertyWrapper_Basic.swift

import UIKit

@propertyWrapper
struct Capitalized {

    // MARK: - Properties

    private var value: String

    // MARK: -
    var projectedValue = false
    var wrappedValue: String {
        get {
            value
        }
        set {
            value = newValue.capitalized
            projectedValue = (newValue.count >= 2 && newValue.count <= 32) ? true : false
        }
    }

    // MARK: - Initialization

    init(wrappedValue: String) {
        value = wrappedValue.capitalized
    }

}

@propertyWrapper
struct Capitalized2 {
    var wrappedValue: String {
        didSet {
            wrappedValue = wrappedValue.capitalized
        }
    }
}

@propertyWrapper
struct Uppercased {
    var wrappedValue: String {
        didSet {
            wrappedValue = wrappedValue.uppercased()
        }
    }
}

@propertyWrapper
struct MyDouble<T:Numeric> {
    private var value: T

    var wrappedValue: T {
        get {
            value * 2
        }
        set {
            value = newValue
        }
    }
    
    init(wrappedValue: T) {
        self.value = wrappedValue
    }
}


// MARK: - Use In
// -------
struct Book {
    @Capitalized var author: String
    @Capitalized2 var title: String
    @Uppercased var des: String = "a. cád f dsf sd à dsaf"
}

var book = Book(author: "fx studio", title: "a great book")
print(book.author)
book.title.append("!")
print(book.title)

// -------
class SomeClass {
    @MyDouble var count: Float
    @MyDouble var total: Int = 10
    
    init(count: Float) {
        self.count = count
    }
}

var obj = SomeClass(count: 1)
print(obj.count)
print(obj.total)

obj.count = 19
print(obj.count)

// -------
class NewBook {
    @Capitalized var author: String
    @Capitalized var title: String
    
    init(author: String, title: String) {
        self.author = author
        self.title = title
    }
}

var newbook = NewBook(author: "f", title: "a great book2")

print(newbook.author)
print(newbook.$author)

newbook.author.append("x studio")
print(newbook.author)
print(newbook.$author)

newbook.$author = true