LazyOne it's an easy implementation of default lazy keyword based on @propertyWrapper feature.

LazyOne.swift

@propertyWrapper
final class LazyOnce<T> {
    private var storage: T?
    private let lazyBlock: () -> T

    var wrappedValue: T {
        if let existStorage = storage { return existStorage }
        let newStorage = lazyBlock()
        self.storage = newStorage
        return newStorage
    }

    init(wrappedValue: @escaping @autoclosure () -> T) {
        self.lazyBlock = wrappedValue
    }
}

// Usage
final class FooBar {
    lazy var foo = "Test"
    // or
    @LazyOnce var bar = "Test"
}