What is meaning of NSMutableDictionary.lazy in swift?

Question

I am confused about where to use lazy functionality, I mean to say in which type of condition I should use lazy keyword in the collection.

Answer 1

From Apple Docs:

A lazy stored property is a property whose initial value is not calculated until the first time it is used. You indicate a lazy stored property by writing the lazy modifier before its declaration.

When use @lazy property then remembers below things:

• Lazy property must always declare with the var keyword, not with the let constant.
• Lazy properties must be initialized when it is declared.

---

How we achieve lazy functionality in Objective-C

@property (nonatomic, strong) NSMutableArray *players;

- (NSMutableArray *)players 
{
    if (!_players) {
        _players = [[NSMutableArray alloc] init];
    }
    return _players;
}

---

And now in Swift, you can achieve the same functionality by using lazy property. See below example

class Person {

    var name: String

    lazy var personalizedGreeting: String = {

        return "Hello, \(self.name)!"
    }()

    init(name: String) {
        self.name = name
    }
}

Now when you initialize a person, their personal greeting hasn’t been created yet:

let person = Person(name: "John Doe")  // person.personalizedGreeting is nil

But when you attempt to print out the personalized greeting, it’s calculated on-the-fly:

print(person.personalizedGreeting)
// personalizedGreeting is calculated when used
// and now contains the value "Hello, John Doe!"

I hope this will help you to understand the functionality of lazy property.