Name:
  Flyweight

Intent:
  - share equal instances (copies) of a some class of interest
    (share as opposed to construct new equal copies)

Structure:
  - when an object is constructed, save a reference
  - the reference is saved in a central repository
  - when a object is needed, check the repository, and
    if it has been constructed already, return the reference
    without constructing.
  - Flyweight objects may be immutable
  - Flyweight class should be a singleton

Notes:
  - related to factories
  - ObjectPool