See: nested records (Dr Okie's notes)
  - a record (`Point`),
  - a record-of-records (`Line`), and
  Code from class: employees_v1.adb



  - an array-of-record-of-records (`LineList`)


  ibarland's particular reminders re presentation:

   record Point (and initializer, by posn and by name)
      make diagram closer to the raw row-of-mem-locs;
      use dotted-line between fields, and on right use `}`
      reminder: access fields via `.`
   record Line  (initialize using 2 vars, and initialize using literals)
      make diagram closer to the raw row-of-mem-locs;
      use squiggle-line between its two fields, and on right use nested `}`
   draw a mem-diagram of array-of-Line (as one big mem chunk)
    THEN ask: how do we refer to [this cell here]; answer: lines(2).start.y
    

  The mostly-analagous Java:
  see NestedRecords.java


  

  What if we make an array of 10 Employees, and read in/fill only 3 of them?
  We can do this, but we need to track how many of the array-locations represent "real" data.
  (This is how ArrayList works -- an array which is only partially full.
     Though it has two additional aspects: re-sizing on inserts,
     and it's fully encapsulated as an Abstract Data Type `List`.
     We say that internally ArrayList uses a "backing array".)

  See:
  employees_v2.adb (the backing array, and separately track the count)
  and then
  employees_v3.adb (combine these two related pieces into one record/object/struct)