SpecialCase

Last edit April 6, 2006

A generalization of NullObject.

Represent special values with an object of distinguished class.

For example:

  Date (or Timestamp) -> Past & Future - special cases that are before (after) every other date.

  Date (or Timestamp) -> Now - continuously updates

  Money -> Zero - an object representing no monetary value

Combining the date special cases with TimeInterval results in some interesting possibilities.

SpecialCase is really a SpecialCase of ObjectOriented programming in general just applied to some well known base types, isn't it? Consider Boolean in SmallTalk. True and False are just special cases.

CategoryPattern