Pamiątka

Pamiątka w języku Rust

Pamiątka to behawioralny wzorzec projektowy umożliwiający zapisywanie “migawek” stanu obiektu i późniejsze jego przywracanie.

Wzorzec Pamiątka nie wpływa na wewnętrzną strukturę obiektu z którym współpracuje, ani na dane przechowywane w migawkach.

Dowiedz się więcej o Pamiątka

Conceptual example

This is a conceptual example of Memento pattern.

conceptual.rs

trait Memento<T> {
    fn restore(self) -> T;
    fn print(&self);
}

struct Originator {
    state: u32,
}

impl Originator {
    pub fn save(&self) -> OriginatorBackup {
        OriginatorBackup {
            state: self.state.to_string(),
        }
    }
}

struct OriginatorBackup {
    state: String,
}

impl Memento<Originator> for OriginatorBackup {
    fn restore(self) -> Originator {
        Originator {
            state: self.state.parse().unwrap(),
        }
    }

    fn print(&self) {
        println!("Originator backup: '{}'", self.state);
    }
}

fn main() {
    let mut history = Vec::<OriginatorBackup>::new();

    let mut originator = Originator { state: 0 };

    originator.state = 1;
    history.push(originator.save());

    originator.state = 2;
    history.push(originator.save());

    for moment in history.iter() {
        moment.print();
    }

    let originator = history.pop().unwrap().restore();
    println!("Restored to state: {}", originator.state);

    let originator = history.pop().unwrap().restore();
    println!("Restored to state: {}", originator.state);
}

Output

Originator backup: '1'
Originator backup: '2'
Restored to state: 2
Restored to state: 1

Serde serialization framework

A common way to make a structure serializable is to derive Serialize and Deserialize traits from the serde serialization framework. Then an object of serializable type can be converted to many different formats, e.g. JSON with serde_json crate.

use serde::{Deserialize, Serialize};

#[derive(Serialize, Deserialize)]
struct Originator {
    state: u32,
}

serde.rs

use serde::{Deserialize, Serialize};

/// An object to be stored. It derives a default
/// `Serialize` and `Deserialize` trait implementation, which
/// allows to convert it into many different formats (e.g. JSON).
#[derive(Serialize, Deserialize)]
struct Originator {
    state: u32,
}

impl Originator {
    /// Serializes an originator into a string of JSON format.
    pub fn save(&self) -> String {
        serde_json::to_string(self).unwrap()
    }

    /// Deserializes an originator into a string of JSON format.
    pub fn restore(json: &str) -> Self {
        serde_json::from_str(json).unwrap()
    }
}

fn main() {
    // A stack of mementos.
    let mut history = Vec::<String>::new();

    let mut originator = Originator { state: 0 };

    originator.state = 1;
    history.push(originator.save());

    originator.state = 2;
    history.push(originator.save());

    for moment in history.iter() {
        println!("{}", moment);
    }

    let originator = Originator::restore(&history.pop().unwrap());
    println!("Restored to state: {}", originator.state);

    let originator = Originator::restore(&history.pop().unwrap());
    println!("Restored to state: {}", originator.state);
}

Output

{"state":1}
{"state":2}
Restored to state: 2
Restored to state: 1

Pamiątka w innych językach