SE-0308 allows Swift to use #if conditions with postfix member expressions. This sounds a bit obscure, but it solves a problem commonly seen with SwiftUI: you can now optionally add modifiers to a view.
For example, this change allows us to create a text view with two different font sizes depending on whether we’re using iOS or another platform:
import SwiftUI
Text("Welcome")
#if os(iOS)
.font(.largeTitle)
#else
.font(.headline)
#endifYou can nest these if you want, although it’s a bit hard on your eyes:
Text("Welcome")
#if os(iOS)
.font(.largeTitle)
#if DEBUG
.foregroundColor(.red)
#endif
#else
.font(.headline)
#endifYou could use wildly different postfix expressions if you wanted:
let result = [1, 2, 3]
#if os(iOS)
.count
#else
.reduce(0, +)
#endif
print(result)Technically you could make result end up as two completely different types if you wanted, but that seems like a bad idea. What you definitely can’t do is use other kinds of expressions such as using + [4] instead of .count – if it doesn’t start with . then it’s not a postfix member expression.
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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
- Interchangeable use of CGFloat and Double types
- Codable synthesis for enums with associated values
- lazy now works in local contexts
- 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
