concepts: Add alternative Post implementation with states as types

[learn-rust.git] / concepts / src / lib.rs

diff --git a/concepts/src/lib.rs b/concepts/src/lib.rs
index bb15eeb814ea45d9aee64ed43497f586df33ba65..5f1feea9404c8116e1cbb1106b825e5a6d52c677 100644 (file)
--- a/concepts/src/lib.rs
+++ b/concepts/src/lib.rs
@@ -137,11 +137,16 @@ impl Post {
     pub fn approve(&mut self) {
         self.state = self.state.approve();
     }
+
+    pub fn reject(&mut self) {
+        self.state = self.state.reject();
+    }
 }
 
 trait State {
     fn request_review(&self) -> Box<dyn State>;
-    fn approve(&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 {
@@ -152,23 +157,38 @@ trait State {
 struct Draft {}
 impl State for Draft {
     fn request_review(&self) -> Box<dyn State> {
-        Box::new(PendingReview {})
+        Box::new(PendingReview {acks: 0})
     }
 
-    fn approve(&self) -> Box<dyn State> {
+    fn approve(&mut self) -> Box<dyn State> {
         // don't change state
         Box::new(Self {})
     }
+
+    fn reject(&self) -> Box<dyn State> {
+        Box::new(Self {})
+    }
+}
+
+struct PendingReview {
+    acks: u32,
 }
 
-struct PendingReview {}
 impl State for PendingReview {
     fn request_review(&self) -> Box<dyn State> {
-        Box::new(Self {})
+        Box::new(Self {acks: self.acks})
     }
 
-    fn approve(&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 {})
     }
 }
 
@@ -178,11 +198,58 @@ impl State for Published {
         Box::new(Self {})
     }
 
-    fn approve(&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}
+    }
+}