Bijective associative memory. As for ordinary DICTIONARY, Values of type V_ are stored using Keys
of type K_, but, in a BIJECTIVE_DICTIONARY, given one value of type V_, you can retrieve the unique
corresponding key of type K_. In other words, with a BIJECTIVE_DICTIONARY, one key of type K_ gives
you access to one value of type V_ which can be used to retrieve back the same unique original key.
See also DICTIONARY class if you do not have a unique value for each key. By the way, also note that
the interface of DICTIONARY is similar to the interface of BIJECTIVE_DICTIONARY in order to allow you to
move from one to the other.
Approximation of the actual internal storage capacity.
The capacity will grow automatically
when needed (i.e. capacity is not a limit for the number of values stored). Also note that
the capacity value may not be always accurate depending of the implementation (anyway, this
capacity value is at least equals to count).