Undo

An undo/redo library with dynamic dispatch, state handling and automatic command merging.

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.

Examples

toml [dependencies] undo = "0.6.0"

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

[derive(Clone, Copy)]

struct PopCmd { vec: *mut Vec, e: Option, }

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(())

} ```