What problem does this solve or what need does it fill?

Currently FilteredEntityRef look like this:

  /// Gets access to the component of type `T` for the current entity.
  /// Returns `None` if the entity does not have a component of type `T`.
  #[inline]
  pub fn get<T: Component>(&self) -> Option<&'_ T>;

The docstring is incorrect, you get a None if the entity does not have a component of type T OR if the FilteredEntityRef does not have the access to read T.

The return value of Option makes it impossible to distinguish between the two.

I have multiple times been stuck debugging while my entity does not have a given component T only to realize an hour later that my FilteredEntityRef does not have the correct access!!

What solution would you like?

Change the methods to return a Result, where the Errors could be an enum with:

• InsufficientAccess
• ComponentNotFound