Crate undo [−] [src]

An undo/redo library.

About

It uses the Command Pattern where the user implements the UndoCmd trait for each command.

The UndoStack has two states, clean and dirty. The stack is clean when no more commands can be redone, otherwise it is dirty. The stack will notice when it's state changes to either dirty or clean, and call the user defined methods set in on_clean and on_dirty. This is useful if you want to trigger some event when the state changes, eg. enabling and disabling buttons in an ui.

It also supports automatic merging of commands with the same id.

Redo vs Undo

	Redo	Undo
Dispatch	Static	Dynamic
State Handling	Yes	Yes
Command Merging	Yes (manual)	Yes (automatic)

undo uses dynamic dispatch instead of static dispatch to store the commands, which means it has some additional overhead compared to redo. However, this has the benefit that you can store multiple types of commands in a UndoStack at a time. Both supports state handling and command merging but undo will automatically merge commands with the same id, while in redo you need to implement the merge method yourself.

I recommend using undo by default and to use redo when performance is important. They have similar API, so it should be easy to switch between them if necessary.

Examples

use undo::{self, UndoCmd, UndoStack};

#[derive(Clone, Copy)]
struct PopCmd {
    vec: *mut Vec<i32>,
    e: Option<i32>,
}

impl UndoCmd for PopCmd {
    type Err = ();

    fn redo(&mut self) -> undo::Result<()> {
        self.e = unsafe {
            let ref mut vec = *self.vec;
            vec.pop()
        };
        Ok(())
    }

    fn undo(&mut self) -> undo::Result<()> {
        unsafe {
            let ref mut vec = *self.vec;
            let e = self.e.ok_or(())?;
            vec.push(e);
        }
        Ok(())
    }
}

fn foo() -> undo::Result<()> {
    let mut vec = vec![1, 2, 3];
    let mut stack = UndoStack::new();
    let cmd = PopCmd { vec: &mut vec, e: None };

    stack.push(cmd)?;
    stack.push(cmd)?;
    stack.push(cmd)?;

    assert!(vec.is_empty());

    stack.undo()?;
    stack.undo()?;
    stack.undo()?;

    assert_eq!(vec.len(), 3);
    Ok(())
}

An unsafe implementation of redo and undo is used in examples since it is less verbose and makes the examples easier to follow.

Structs

Id	An unique id for an `UndoStack`.
UndoGroup	A collection of `UndoStack`s.
UndoStack	Maintains a stack of `UndoCmd`s.

Traits

UndoCmd

Trait that defines the functionality of a command.

Type Definitions

Result

A specialized Result that does not carry any data on success.