}
pub struct Post {
- state: Option<Box<dyn State>>,
+ state: Box<dyn State>,
content: String,
}
impl Post {
pub fn new() -> Post {
Post {
- state: Some(Box::new(Draft {})),
+ state: Box::new(Draft {}),
content: String::new(),
}
}
}
pub fn content(&self) -> &str {
- // as_ref() converts Option<Box<State>> to Option<&Box<State>>
- // state can never be None, all state transitions return a new one
- self.state.as_ref().unwrap().content(self)
+ self.state.content(self)
}
pub fn request_review(&mut self) {
- if let Some(s) = self.state.take() {
- self.state = Some(s.request_review());
- }
+ self.state = self.state.request_review();
}
pub fn approve(&mut self) {
- if let Some(s) = self.state.take() {
- self.state = Some(s.approve());
- }
+ self.state = self.state.approve();
+ }
+
+ pub fn reject(&mut self) {
+ self.state = self.state.reject();
}
}
trait State {
- fn request_review(self: Box::<Self>) -> Box<dyn State>;
- fn approve(self: Box::<Self>) -> Box<dyn State>;
+ fn request_review(&self) -> Box<dyn State>;
+ fn approve(&mut self) -> Box<dyn State>;
+ fn reject(&self) -> Box<dyn State>;
#[allow(unused_variables)]
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 request_review(&self) -> Box<dyn State> {
+ Box::new(PendingReview {acks: 0})
+ }
+
+ fn approve(&mut self) -> Box<dyn State> {
+ // don't change state
+ Box::new(Self {})
}
- fn approve(self: Box::<Self>) -> Box<dyn State> {
- self
+ fn reject(&self) -> Box<dyn State> {
+ Box::new(Self {})
}
}
-struct PendingReview {}
+struct PendingReview {
+ acks: u32,
+}
+
impl State for PendingReview {
- fn request_review(self: Box::<Self>) -> Box<dyn State> {
- self
+ fn request_review(&self) -> Box<dyn State> {
+ Box::new(Self {acks: self.acks})
}
- fn approve(self: Box::<Self>) -> Box<dyn State> {
- Box::new(Published {})
+ fn approve(&mut self) -> Box<dyn State> {
+ if self.acks >= 1 {
+ Box::new(Published {})
+ } else {
+ Box::new(Self {acks: self.acks + 1})
+ }
+ }
+
+ fn reject(&self) -> Box<dyn State> {
+ Box::new(Draft {})
}
}
struct Published {}
impl State for Published {
- fn request_review(self: Box::<Self>) -> Box<dyn State> {
- self
+ fn request_review(&self) -> Box<dyn State> {
+ Box::new(Self {})
}
- fn approve(self: Box::<Self>) -> Box<dyn State> {
+ fn approve(&mut self) -> Box<dyn State> {
Box::new(Published {})
}
+ fn reject(&self) -> Box<dyn State> {
+ Box::new(Self {})
+ }
+
fn content<'a>(&self, post: &'a Post) -> &'a str {
&post.content
}
}
+
+// state encoded as types; this is the "approved" state
+pub struct TPost {
+ content: String,
+}
+
+impl TPost {
+ pub fn new() -> TPostDraft {
+ TPostDraft {content: String::new()}
+ }
+
+ pub fn content(&self) -> &str {
+ &self.content
+ }
+}
+
+pub struct TPostDraft {
+ content: String,
+}
+
+impl TPostDraft {
+ pub fn add_text(&mut self, text: &str) {
+ self.content.push_str(text);
+ }
+
+ pub fn request_review(self) -> TPostReview {
+ TPostReview {content: self.content}
+ }
+}
+
+pub struct TPostReview {
+ content: String,
+}
+
+impl TPostReview {
+ pub fn approve(self) -> TPost {
+ TPost {content: self.content}
+ }
+
+ pub fn reject(self) -> TPostDraft {
+ TPostDraft {content: self.content}
+ }
+}