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Swift Academy · Lesson

lazy & property observers

Use lazy stored properties for deferred work and observe changes on stored properties with willSet/didSet.

Overview

This lesson focuses on two essentials: lazy stored properties and property observers (willSet/didSet).

lazy property

lazy defers creation until first access. Useful for expensive work or when self is needed.

struct DataLoader {
    lazy var data: [Int] = {
        print("Loading data...")
        return [1, 2, 3]
    }()
}
var loader = DataLoader()
print("before access")
print(loader.data)   // triggers initialization only now

All lessons in this course

  1. Properties & Subscripts
  2. lazy & property observers
  3. Computed properties with get/set
  4. Subscripts for custom indexing
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