state design pattern

Author: monnetchr

Cargo.lock

@@ -1,3 +1,3 @@
 [workspace]
 resolver = "3"
-members = ["basics","course", "guessgame", "intmut", "myutils", "paral"]
+members = ["basics","course", "guessgame", "intmut", "myutils", "paral", "statedesign"]

Cargo.toml

@@ -8,4 +8,5 @@ basics = { path = "../basics" }
 myutils = { path = "../myutils" }
 guessgame = { path = "../guessgame" }
 intmut = { path = "../intmut" }
-paral = { path = "../paral" }
+paral = { path = "../paral" }
+statedesign = { path = "../statedesign" }

course/Cargo.toml

@@ -5,6 +5,7 @@ use myutils::testing;
 use paral::channels;
 use paral::mutex;
 use paral::threads;
+use statedesign;
 
 fn main() {
     basics::basics();
@@ -20,4 +21,6 @@ fn main() {
     threads::demo();
     channels::demo();
     mutex::demo();
+    statedesign::demo();
+    statedesign::demo2();
 }

course/src/main.rs

@@ -0,0 +1,6 @@
+[package]
+name = "statedesign"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]

statedesign/Cargo.toml

@@ -0,0 +1,24 @@
+mod post;
+use post::Post;
+
+pub fn demo() {
+    println!("This is the state design pattern demo.");
+    let mut post = Post::new();
+    post.add_text("I ate a salad for lunch today.");
+    assert_eq!("", post.content());
+    post.request_review();
+    assert_eq!("", post.content());
+    post.approve();
+    assert_eq!("I ate a salad for lunch today.", post.content());
+}
+
+mod post2;
+
+pub fn demo2() {
+    println!("This is the state design pattern demo2.");
+    let mut post = post2::Post::new();
+    post.add_text("I ate a salad for lunch today.");
+    let post = post.request_review();
+    let post = post.approve();
+    assert_eq!("I ate a salad for lunch today.", post.content());
+}

statedesign/src/lib.rs

@@ -0,0 +1,73 @@
+pub struct Post {
+    content: String,
+    state: Option<Box<dyn State>>,
+}
+
+impl Post {
+    pub fn new() -> Post {
+        Post {
+            content: String::new(),
+            state: Some(Box::new(Draft {})),
+        }
+    }
+    pub fn add_text(&mut self, text: &str) {
+        self.content.push_str(text);
+    }
+    pub fn content(&self) -> &str {
+        self.state.as_ref().unwrap().content(self)
+    }
+    pub fn request_review(&mut self) {
+        if let Some(state) = self.state.take() {
+            self.state = Some(state.request_review());
+        }
+    }
+    pub fn approve(&mut self) {
+        if let Some(state) = self.state.take() {
+            self.state = Some(state.approve());
+        }
+    }
+}
+
+trait State {
+    fn request_review(self: Box<Self>) -> Box<dyn State>;
+    fn approve(self: Box<Self>) -> Box<dyn State>;
+    fn content<'a>(&self, _post: &'a Post) -> &'a str {
+        ""
+    }
+}
+
+struct Draft {}
+
+impl State for Draft {
+    fn request_review(self: Box<Self>) -> Box<dyn State> {
+        Box::new(PendingReview {})
+    }
+    fn approve(self: Box<Self>) -> Box<dyn State> {
+        self
+    }
+}
+
+struct PendingReview {}
+
+impl State for PendingReview {
+    fn request_review(self: Box<Self>) -> Box<dyn State> {
+        self
+    }
+    fn approve(self: Box<Self>) -> Box<dyn State> {
+        Box::new(Published {})
+    }
+}
+
+struct Published {}
+
+impl State for Published {
+    fn request_review(self: Box<Self>) -> Box<dyn State> {
+        self
+    }
+    fn approve(self: Box<Self>) -> Box<dyn State> {
+        self
+    }
+    fn content<'a>(&self, post: &'a Post) -> &'a str {
+        &post.content
+    }
+}

statedesign/src/post.rs

@@ -0,0 +1,36 @@
+pub struct Post {
+    content: String,
+}
+impl Post {
+    pub fn new() -> DraftPost {
+        DraftPost {
+            content: String::new(),
+        }
+    }
+    pub fn content(&self) -> &str {
+        &self.content
+    }
+}
+pub struct DraftPost {
+    content: String,
+}
+impl DraftPost {
+    pub fn add_text(&mut self, text: &str) {
+        self.content.push_str(text);
+    }
+    pub fn request_review(self) -> PendingReviewPost {
+        PendingReviewPost {
+            content: self.content,
+        }
+    }
+}
+pub struct PendingReviewPost {
+    content: String,
+}
+impl PendingReviewPost {
+    pub fn approve(self) -> Post {
+        Post {
+            content: self.content,
+        }
+    }
+}