@EnvironmentObject and Protocols?

Question

below OP

Created Mar ’21

Replies 2

Boosts 1

Views 4.9k

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I would like to declare an @EnvironmentObject as a protocol, namely as

Code Block protocol AccessTokenProvider: Authenticator {
    func accessToken() -> AccessTokenPublisher
}

where Authenticator is

Code Block public class Authenticator: NSObject, ObservableObject

However, when I add this to the environment as

Code Block var authenticator: AccessTokenProvider = MyAuthenticator()
[…]
ContentView().environmentObject(authenticator)

the compiler throws an error at:

Code Block struct ContentView: View {
// error: property type 'AccessTokenProvider' does not match that of the 'wrappedValue' property of its wrapper type 'EnvironmentObject'
    @EnvironmentObject var authenticator: AccessTokenProvider
                           ^

Is this even a good idea? If so, what am I doing wrong?
^

Answered by OOPer in 666610022

what am I doing wrong?

The type of @EnvirontmentObject must conform to ObservableObject.
But, in Swift, usual protocols used as type cannot conform to any protocols.
(In your declaration of AccessTokenProvider, : Authenticator works as a requirement of the protocol, but it does not mean AccessTokenProvider conforming to ObservableObject.)

Under the current restriction of the type system of Swift, you cannot use protocol type for @EnvirontmentObject.

You can start some discussion about this in forums.swift.org .

Boost

Answer 1

OOPer OP

Mar ’21

Accepted Answer

what am I doing wrong?

The type of @EnvirontmentObject must conform to ObservableObject.
But, in Swift, usual protocols used as type cannot conform to any protocols.
(In your declaration of AccessTokenProvider, : Authenticator works as a requirement of the protocol, but it does not mean AccessTokenProvider conforming to ObservableObject.)

Under the current restriction of the type system of Swift, you cannot use protocol type for @EnvirontmentObject.

You can start some discussion about this in forums.swift.org .

1

Answer 2

franmowinckel OP

Apr ’22

You can just use some generics:

public protocol Authenticator: ObservableObject {}
public protocol AccessTokenProvider: Authenticator {}

struct YourView<Provider>: View where Provider: AccessTokenProvider {
    @EnvironmentObject var authenticator: Provider

    var body: some View {
        EmptyView()
    }

}

1