Memento: "classic" and serde implementations

Author: fadeevab

Cargo.toml

@@ -20,4 +20,5 @@ members = [
   "behavioral/command",
   "behavioral/iterator",
   "behavioral/mediator",
+  "behavioral/memento",
 ]

behavioral/memento/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+edition = "2021"
+name = "memento"
+version = "0.1.0"
+
+[[bin]]
+name = "memento"
+path = "classic.rs"
+
+[[bin]]
+name = "memento-serde"
+path = "serde.rs"
+
+[dependencies]
+serde = {version = "1.0", features = ["derive"]}
+serde_json = "1.0"

behavioral/memento/README.md

@@ -0,0 +1,35 @@
+# Memento
+
+## `classic.rs`
+
+A conceptual example of Memento pattern.
+
+```bash
+cargo run --bin memento
+```
+
+Output:
+
+```
+Originator backup: '1'
+Originator backup: '2'
+Restored to state: 2
+Restored to state: 1
+```
+
+## `serde.rs`
+
+A Memento example implemented via serialization with `serde` crate which is pretty popular in Rust.
+
+```bash
+cargo run --bin memento-serde
+```
+
+Output:
+
+```
+{"state":1}
+{"state":2}
+Restored to state: 2
+Restored to state: 1
+```

behavioral/memento/classic.rs

@@ -0,0 +1,54 @@
+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);
+}

behavioral/memento/serde.rs

@@ -0,0 +1,39 @@
+
+use serde::{Serialize, Deserialize};
+
+#[derive(Serialize, Deserialize)]
+struct Originator {
+    state: u32,
+}
+
+impl Originator {
+    pub fn save(&self) -> String {
+        serde_json::to_string(self).unwrap()
+    }
+
+    pub fn restore(json: &str) -> Self {
+        serde_json::from_str(json).unwrap()
+    }
+}
+
+fn main() {
+    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);
+}