Stop Treating Size Class As Screen Width In SwiftUI

This article discusses the pitfalls of using `@Environment(\.horizontalSizeClass)` as a shortcut for determining screen width in SwiftUI, particularly in light of iOS apps becoming resizable for larger displays, iPad, and iPhone Mirroring on Mac. It argues that size class is a trait, not a measure of actual view width, and provides examples of how branching on size class can lead to incorrect layouts. The post offers alternatives like GeometryReader, ViewThatFits, and NavigationSplitView, and includes a code example of a mailbox-style UI that needs auditing. It emphasizes using available size of the surrounding view for finer control, referencing WWDC26 sessions and Xcode 27 features.