fasterKeys

This was taking some time in publishing and we didn't really need a Set

keyAtValue:ifAbsent:

Answer the key that is the external name for the argument, value. If
there is none, answer the result of evaluating exceptionBlock.

keys

Answer a Set containing the receiver's keys.

scanFor:

Scan the key array for the first slot containing either a nil (indicating an empty slot) or an element that matches anObject. Answer the index of that slot or zero if no slot is found. This method will be overridden in various subclasses that have different interpretations for matching elements.