if for postfix member expressions
if for postfix member expressions 관련
Available from Swift 5.5
SE-0308 (apple/swift-evolution) 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)
#endif
You 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)
#endif
You 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.
Other Changes in Swift 5.5