Don't use anything from System.Reflection namespace in Update() loop

[originalfoo]

Problem statement

This is disturbingly common in commuinity submitted mods, especially small "that couldn't possibly be the cause of the lag" mods:

public class DecimateFps : MonoBehaviour
{
   protected void Update()
   {
        // Code using `System.Reflection` to get/set private properies
   }
}

Is also disastrous in LateUpdate(), OnGUI(), etc.

Often the System.Reflection code will be contained in a separate method - I'm not sure if the analyzer can track that down? Such methods often have a signature similar to Q ReadPrivate<T, Q>(T o, string fieldName) or WritePrivate<T, Q>(T o, string fieldName, object value).

Proposed solution

No code fix suggestion for this, it just needs flagging to user as a warning.

Performance: Never use System.Reflection features in performance critical messages.

Docs could mention:

If you must use System.Reflection to access a private member, consider caching FieldInfo or MethodInfo in Start(), or elsewhere, and use the cached references in the loop instead.

In many cases alternatives are available which don't require reflection. For example, if a game object has a private field referencing a UI component, a direct reference to the component can be obtained using code such as FindObjectOfType<SomeGO>().GetComponent<T>(); the component can be cached and subsequently directly accessed in the update loop.

[sailro]

Yes we are thinking as well on doing this kind of analysis.