SwiftConformableExistential

A set of Swift Macros designed to facilitate the conformance of existential types to Equatable, Hashable, Decodable, Encodable, and Codable.

Overview

Until Swift gains support for extending existential types, they cannot satisfy generic constraints on their own.

protocol Drinkable: Hashable {}

// Is ill-formed, because `any Drinkable` does not conform to `Hashable`,
// despite the fact that every `Drinkable` instance does.
struct Foo: Hashable {
    let drinkable: any Drinkable
}

Overcoming this limitation requires extensive boilerplate code. This package offers a set of macros that can be attached to your protocol to synthesize ready-to-use property wrappers over the existential type of the annotated protocol. These wrappers act as proxies for the respective conformances.

import SwiftConformableExistential

@HashableExistential
protocol Drinkable: Hashable {}

// `HashableDrinkable` is a `Hashable` wrapper over `any Drinkable`,
// synthesized of the attached `@HashableExistential` macro,
// allowing the compiler to now synthesize the `Hashable` implementation for `Foo`.
struct Foo: Hashable {

    @HashableDrinkable
    var drinkable: any Drinkable
}

Alternatively, the wrappers can also be used on-the-fly, particularly in situations where employing property wrappers is not suitable:

struct Tap: View {

    @State private var drinkable: any Drinkable = .smallBeer
    
    var body: some View {
        ...           
        .onChange(of: HashableDrinkable(drinkable)) { _, newValue in
            prepareForPouring(newValue.wrappedValue)
        }
    }
}

For more, see the documentation.

Installation

Via SwiftPM.

In your package dependencies:

.package(url: "https://github.com/stansmida/swift-conformable-existential.git", from: "0.4.0"),

And in your target dependencies:

.product(name: "SwiftConformableExistential", package: "swift-conformable-existential"),

And don't forget to import in files where annotating your protocols:

import SwiftConformableExistential