The lazy keyword has always allowed us to write stored properties that are only calculated when first used, but from Swift 5.5 onwards we can use lazy locally inside a function to create values that work similarly.
This code demonstrates local lazy in action:
func printGreeting(to: String) -> String {
print("In printGreeting()")
return "Hello, \(to)"
}
func lazyTest() {
print("Before lazy")
lazy var greeting = printGreeting(to: "Paul")
print("After lazy")
print(greeting)
}
lazyTest()When that runs you’ll see “Before lazy” and “After lazy” printed first, followed by “In printGreeting()” then “Hello, Paul” – Swift only runs the printGreeting(to:) code when its result is accessed on the print(greeting) line.
In practice, this feature is going to be really helpful as a way of selectively running code when you have conditions in place: you can prepare the result of some work lazily, and only actual perform the work if it’s still needed later on.
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Other changes in Swift 5.5…
- Async await
- Async sequences
- Effectful read-only properties
- Structured concurrency
- async let bindings
- Continuations for interfacing async tasks with synchronous code
- Actors
- Global actors
- Sendable and @Sendable closures
- if for postfix member expressions
- Interchangeable use of CGFloat and Double types
- Codable synthesis for enums with associated values
- Extending property wrappers to function and closure parameters
- Extending static member lookup in generic contexts
Download all Swift 5.5 changes as a playground Link to Swift 5.5 changes
