Trait redo::Command

pub trait Command<R> {
    type Error;
    fn apply(&mut self, receiver: &mut R) -> Result<(), Self::Error>;
    fn undo(&mut self, receiver: &mut R) -> Result<(), Self::Error>;

    fn redo(&mut self, receiver: &mut R) -> Result<(), Self::Error> { ... }
    fn merge(&mut self, command: Self) -> Merge<Self>
    where
        Self: Sized,
    { ... }
}

Base functionality for all commands.

Associated Types

type Error

The error type.

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Required methods

fn apply(&mut self, receiver: &mut R) -> Result<(), Self::Error>

Applies the command on the receiver and returns Ok if everything went fine, and Err if something went wrong.

fn undo(&mut self, receiver: &mut R) -> Result<(), Self::Error>

Restores the state of the receiver as it was before the command was applied and returns Ok if everything went fine, and Err if something went wrong.

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Provided methods

fn redo(&mut self, receiver: &mut R) -> Result<(), Self::Error>

Reapplies the command on the receiver and return Ok if everything went fine, and Err if something went wrong.

The default implementation uses the apply implementation.

fn merge(&mut self, command: Self) -> Merge<Self> where
    Self: Sized, 

Used for manual merging of two commands.

Examples

struct Add(String);

impl Command<String> for Add {
    type Error = ();

    fn apply(&mut self, s: &mut String) -> Result<(), ()> {
        s.push_str(&self.0);
        Ok(())
    }

    fn undo(&mut self, s: &mut String) -> Result<(), ()> {
        let len = s.len() - self.0.len();
        s.truncate(len);
        Ok(())
    }

    fn merge(&mut self, Add(s): Self) -> Merge<Self> {
        self.0.push_str(&s);
        Merge::Yes
    }
}

fn main() -> Result<(), ()> {
    let mut record = Record::default();
    // The `a`, `b`, and `c` commands are merged.
    record.apply(Add("a".into()))?;
    record.apply(Add("b".into()))?;
    record.apply(Add("c".into()))?;
    assert_eq!(record.as_receiver(), "abc");
    // Calling `undo` once will undo all the merged commands.
    record.undo().unwrap()?;
    assert_eq!(record.as_receiver(), "");
    // Calling `redo` once will redo all the merged commands.
    record.redo().unwrap()?;
    assert_eq!(record.as_receiver(), "abc");
    Ok(())
}

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Implementors

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