Crate undo_stack

Work in Progress. Currently does not work outside project it was created for. A Minimalistic Undo/Redo library created for personal projects. Use at your own risk!

Whenever your application data changes to a new value, you can push the old value into the UndoStack using the UndoStack::push method. Calling UndoStack::undo will walk through the stack returning past_stack values, but possible values above the current position are still available via the UndoStack::redo method, which will cause the stack to walk back into the present.

Calling undo and then pushing a new value clears the redo stack, since history was rewritten and now the future_stack state will be different.

When calling undo and redo, the restored values are automatically restored to an associated Project type (the struct containing the data) via the Undoable trait, which simply contains a “restore” method where you must provide a way for the restored value to be re-applied to the Project type.

Creating undo values for continuous changes.

A common case in applications with GUIs is a value that needs to be udpdated continuously on the screen while the user interacts with it (i.e. dragging a slider), but only its initial state and final will be used for undo purposes.

You can easily achieve this using the UndoStack::start_buffer and [UndoStack::commit_buffer] methods at the beginning and end of the user interaction, instead of “push”. The final state is only used to compare with the initial state, and nothing is actually stored if they’re the same.

Motivation.

I created this crate for personal use, and to satisfy a few requirements I wished for:

• As minimal as possible while still being useful.
• Does not force unwanted programming patterns, i.e. Command pattern.
• Undo values can be stored in multiple stacks, if needed. A use case for this can be seen in modern 3D Animation software, where the Scene undo is usually separated from the Viewport undo.
• Provides a simple trait (Undoable) with a single “restore” method that allows automatically re-applying the restored value to the application data.

Example

Please download the repo and run “cargo run -p example” at the project root for a simple demonstration. The example is located under the “example” subfolder.

Structs

• UndoStack
  The main struct where all the undo values are kept.

Traits

• Undoable
  When calling undo() or redo(), the restore() function is always called and applies this value TO the project and returns a value with the previous state FROM the project. The “Undoable” type, usually an enum with many variants, needs to know how to restore itself, and may need to contain all information required to place it correctly into the project.