A novel use of SwiftPM traits can strike a nice balance between soft and hard deprecations, giving users a friendly migration path towards major breaking changes. We explore this concept in the context of our upcoming Composable Architecture 2.0 release.

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SwiftPM traits can be used for library evolution by enabling a two-tier deprecation strategy. By default, APIs are 'soft' deprecated (silently marked in docs and the type system), while an opt-in trait upgrades them to hard compiler warnings. Point-Free is applying this pattern in Composable Architecture 1.25 via the `ComposableArchitecture2Deprecations` trait, letting users incrementally prepare for the upcoming 2.0 major release. Specific API changes include `Effect<Action>` becoming `EffectOf<Feature>`, `Send<Action>` becoming `SendOf<Feature>`, and a revised `onChange` API. Instructions are provided for enabling the trait in both `Package.swift` and Xcode 26.4+.

Hard Deprecations and Soft Landings with SwiftPM Traits