Because CompiledFunctions extends TreeSet to store specialized functions and CompiledFunction only uses its method type weight to implement Comparable.compareTo(), a CompiledFunction will replace any other CompiledFunction with the same weight present in the TreeSet.

To allow storing multiple functions with the same weight (e.g. (int,int) and (double)) compareTo() needs to be consistent with equals(), i.e. it must only return 0 if objects are equal.