Undo

Undo ( make English for take back, return ) or Undo ( make ), Take Back or withdrawal refers to the function of application programs that may be redeemed with the one or more actions. Depending on the scope of the application can undo possibility of the withdrawal of the last action extend to the withdrawal of all work steps. The Undo function is often combined with a redo function that cancels a previous undo.

History

An undo function was first proposed published by IBM employees Lance A. Miller and John C. Thomas in her 1977 essay Behavioral Issues in the Use of Interactive Systems ( behavioral issues in the use of interactive systems ). They noted that it would be pretty useful when users are at least " take back " the last command could ( by running a special " Undo" command). Programmer of the research center Xerox PARC occupied the key combination Control Z with an undo command. In this form of the command an indispensable part of editors and word processing programs on personal computers was fast. In the 1980s, multi-level undo commands were introduced.

Implementation

Providing an undo function requires the presence of at least a rudimentary form of versioning. The undo / redo functionality can be implemented by means of the command design pattern.