Method or delegate parameters do not match delegate parameters

Question

I'm doing some asynchronous caching and I'm using a simple Action callback to let the rest of the system know when the caching is complete.

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The entry point (the line causing the error):

this.StartCoroutine<Action>(SceneUtils.CacheSceneNames, PopulateButtons);

Coroutine method:

public static IEnumerator CacheSceneNames(Action completedCallback) {}

Callback method:

private void PopulateButtons() {}

And finally, the method that starts the coroutine:

public static Coroutine StartCoroutine<T>(this MonoBehaviour extends, Func<IEnumerator, T> method, T value) {}

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As far as I can tell all of the parameter and return types are correct, however I'm getting the following error:

error CS0123: A method or delegate `CacheSceneNames(System.Action)' parameters do not match delegate `System.Func<System.Collections.IEnumerator,System.Action>(System.Collections.IEnumerator)' parameters

Can anyone point out what I am doing wrong? Could this be a covariance issue?

Answer 1

I think you want to specify Func<T, IEnumerator> method instead of Func<IEnumerator, T> method in the parameter list of StartCoroutine<T> .

It's Func<T, TResult> : the return type is the last type parameter - and your CacheSceneNames takes a parameter of Action ( T ) and returns IEnumerator .