Creates an anonymous MonoBehaviour instance from a given update Action.

AnonymousMonobehaviours.cs

public static class AnonymousMonoBehaviours
{
    private static readonly Action EmptyAction = () => { };

    /// <summary>
    /// Creates an anonymous MonoBehaviour instance from a given update Action.
    /// The instance can be destroyed by calling Dispose on the returned IDisposable.
    /// </summary>
    /// <param name="updateFn">Called whenever AnonymousMonobehaviour.Update() is called.</param>
    /// <param name="startFn">Called whenever AnonymousMonobehaviour.Start() is called.</param>
    /// <param name="onDestroyFn">Called whenever AnonymousMonobehaviour.OnDestroy() is called, i.g. when disposable.Dispose() is called.</param>
    /// <param name="name">The name of the game object that this AnonymousUpdateBehaviour will create</param>
    /// <returns>A disposable allowing the caller to destroy this anonymous instance.</returns>
    public static IDisposable Update(Action updateFn, Action startFn = null, Action onDestroyFn = null, string name = "AnonymousUpdateBehaviour")
    {
        var g = GameObject.Instantiate(new GameObject()) as GameObject;
        g.name = name;
        var b = g.AddComponent<AnonymousUpdateBehaviour>();

        b.StartFn = startFn ?? EmptyAction;
        b.UpdateFn = updateFn;
        b.OnDestroyFn = onDestroyFn ?? EmptyAction;
            
        return Disposable.Create(() => GameObject.Destroy(g));
    }
}
    
    
public class AnonymousUpdateBehaviour : MonoBehaviour
{
    private Action _startFn;
    private Action _onDestroyFn;
    private Action _updateFn;

    public Action UpdateFn
    {
        set { _updateFn = value; }
    }

    public Action StartFn
    {
        set { _startFn = value; }
    }

    public Action OnDestroyFn
    {
        set { _onDestroyFn = value; }
    }

    void Start()
    {
        _startFn();
    }

    void Update()
    {
        _updateFn();
    }

    void OnDestroy()
    {
        _onDestroyFn();
    }
}

Usage.cs

// Example usage:
var d = AnonymousMonoBehaviours.Update(() => Debug.Log("I run in the Unity update loop!"));
// time passes...
d.Dispose();