Generic closures in dependencies

[StefanCosminR]

Hi!

I'm trying to extend one of my dependencies to have a generic parameter an I realised this is not supported by Swift. Is there an easy workaround to do this?

@DependencyClient
public struct UserSettingsClient {
    public var get: (_ key: String) throws -> String?
    public var getBool: (_ key: String) -> Bool?
    public var set: (_ string: String, _ key: String) throws -> Void
    public var setBool: (_ isTrue: Bool, _ key: String) throws -> Void
    public var remove: (_ key: String) throws -> Void
    public var getCodable: (_ value: some Codable) -> Void // this line is not valid
}

Using "some Codable" in that context is not supported. I could convert this to a protocol but then I lose all the advantaged of this technique and I'd probably have to change a lot of existing tests.

Another option I found, which is quite verbose, is to use a struct that implements callAsFunction.

protocol UserSettingsGetCodable {
    func callAsFunction<Value: Codable>(_ key: String) -> Value?
}

struct UserSettingsGetCodableUserDefaults: SecretsGetCodable {
    let userDefaults: UserDefaults
    
    func callAsFunction<Value: Codable>(_ key: String) throws -> Value? {
        // impl
    }
}

@DependencyClient
public struct UserSettingsClient {
    // ... like previous example
    var _getCodable: any UserSettingsGetCodable
    
    public func getCodable<Value>(key: String) -> Value? where Value: Decodable, Value: Encodable {
        _getCodable(key)
    }
}

This works, the change is purely additive but it's very verbose. I wish I could remove UserSettingsSetCodable, but I want to use a different storage in tests and preview (not, UserDefaults)