Снимок — это поведенческий паттерн, позволяющий делать снимки внутреннего состояния объектов, а затем восстанавливать их.
При этом Снимок не раскрывает подробностей реализации объектов, и клиент не имеет доступа к защищённой информации объекта.
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