A state that implements this interface implies that it itself is immutable and the ObjectInstances it uses are immutable.
A State instance is used to define the state of an environment or an observation from the environment.
The FixedSizeImmutableState is an ImmutableState class that will only allow you to set attribute values of specific objects, and assumes that objects themselves remain in the state.
An immutable state cannot be changed (nor subclassed).
State objects are a collection of Object Instances.