https://medium.com/swift-programming/how-to-do-proper-lazy-loading-in-swift-b8bc57dbc7b9

asd.swift

var nonLazyInitializationCalled = 0
var lazyInitializationCalled = 0

class Foo {
  lazy var bar: String = {
    lazyInitializationCalled += 1
    return "bar"
  }()

  var baz: String = {
    nonLazyInitializationCalled += 1
    return "baz"
  }()
}


lazyInitializationCalled // 0
nonLazyInitializationCalled // 0

let a = Foo()
lazyInitializationCalled // 0
nonLazyInitializationCalled // 1

a.bar
a.bar

a.baz
a.baz

lazyInitializationCalled // 1
nonLazyInitializationCalled // 1