Hello all,

I'm trying to create a protocol for something that must also conform to ObservableObject, which will live within another object Services:

protocol ThumbnailServiceProtocol: ObservableObject where ObjectWillChangePublisher == ObservableObjectPublisher {
    var processingThumbnails: [String] { get }
}

final class ThumbnailService: ThumbnailServiceProtocol {
    var processingThumbnails: [String] = []
}

struct Services {
    var thumbnailService: ThumbnailServiceProtocol
}

var services = Services(thumbnailService: ThumbnailService())

My problem comes when I try to swap out services to use a mock in my tests like this:

final class MockThumbnailService: ThumbnailServiceProtocol {
    var processingThumbnails: [String] = []
}

services = Services(thumbnailService: MockThumbnailService()) /// Cannot convert value of type 'MockThumbnailService' to expected argument type 'ThumbnailService'

I think the problem is coming from the fact that ObservableObject is a protocol with an associated type (associatedtype ObjectWillChangePublisher) but I thought I'd 'filled in the hole' by specifying where ObjectWillChangePublisher == ObservableObjectPublisher.

Am I missing something please?