My Editor Design

Lecture Notes for CS 190
Spring 2016
John Ousterhout

• Text.Tracker:
  • General-purpose mechanism, used for several different things.
• TrackedPosition class:
  • Subclass of Position
  • Automatically updates when text is modified:
    • Sticks to character at that position (inserts <= this position push it out)

• No need to worry about cursor and selection changing location because of text modifications.
  • Selection is always valid, but may be empty
• UndoText: automatically makes text undoable.
  • Keeps track of undos in progress, so it won't record new entries for undo/redo operations.

• Undo grouping:
  • Set fences when the insertion cursor is moved
  • Don't need many other fences
  • Still not ideal; may not scale well as new functions are added