Using `cancellable` creates build error "Type of expression is ambiguous without more context"

Fogmeister · 2022-05-16T13:45:55.040Z

In my reducer switch I have it like...

enum WelcomeRequestId {}

switch action {
case .fetchContent:
	return environment.welcomeScreenClient.fetchContent()
		.receive(on: environment.main)
		.catchToEffect(WelcomeScreenAction.contentResponse)
//		.cancellable(id: WelcomeRequestId.self, cancelInFlight: true)

This builds.

But... if I uncomment the last line in this case I get a build error...

Type of expression is ambiguous without more context

In the auto complete it is showing the correct type so I'm not sure now what it is that I've done wrong.

Any ideas?

Thanks

stephencelis · 2022-05-16T14:00:49.502Z

Using types as cancel identifiers is a new feature that we still haven't cut a version for. In the meantime, you can use the older style:

struct WelcomeRequestId: Hashable {}

// And then:

.cancellable(id: WelcomeRequestId(), cancelInFlight: true)

We'll try to cut a new version soon, though!

Fogmeister · 2022-05-16T14:03:07.610Z

Ah ok, thanks.

I think maybe the example code might need to be updated...

github.com

pointfreeco/swift-composable-architecture/blob/main/Examples/CaseStudies/SwiftUICaseStudies/02-Effects-Cancellation.swift

import Combine
import ComposableArchitecture
import SwiftUI

private let readMe = """
  This screen demonstrates how one can cancel in-flight effects in the Composable Architecture.

  Use the stepper to count to a number, and then tap the "Number fact" button to fetch \
  a random fact about that number using an API.

  While the API request is in-flight, you can tap "Cancel" to cancel the effect and prevent \
  it from feeding data back into the application. Interacting with the stepper while a \
  request is in-flight will also cancel it.
  """

// MARK: - Demo app domain

struct EffectsCancellationState: Equatable {
  var count = 0
  var currentFact: String?

This file has been truncated. show original

stephencelis · 2022-05-16T14:04:36.913Z

Fogmeister:

I think maybe the example code might need to be updated...

https://github.com/pointfreeco/swift-composable-architecture/blob/main/Examples/CaseStudies/SwiftUICaseStudies/02-Effects-Cancellation.swift

This is example code on the main branch, which we try to keep up-to-date with any changes on main. You can check out the 0.34.0 version of this code here.

Fogmeister · 2022-05-16T14:36:33.846Z

Ah! I see.

I hadn't realised.

Thanks again for the help.

stephencelis · 2022-05-16T19:38:55.447Z

By the way, we just release 0.35.0, so you can update to the new style today