0x00 Lesson
As a performance optimization, Swift lets you create some properties only when they are needed. As an example, consider this FamilyTree struct - it doesn’t do much, but in theory creating a family tree for someone takes a long time:
struct FamilyTree {
init() {
print("Creating family tree!")
}
}
We might use that FamilyTree struct as a property inside a Person struct, like this:
struct Person {
var name: String
var familyTree = FamilyTree()
init(name: String) {
self.name = name
}
}
var ed = Person(name: "Ed")
But what if we didn’t always need the family tree for a particular person? If we add the lazy keyword to the familyTree property, then Swift will only create the FamilyTree struct when it’s first accessed:
lazy var familyTree = FamilyTree()
So, if you want to see the “Creating family tree!” message, you need to access the property at least once:
ed.familyTree
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