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 923b80b451cbe86402e4c649859da5705c11d878..5f1feea9404c8116e1cbb1106b825e5a6d52c677 100644 (file)
--- a/concepts/src/lib.rs
+++ b/concepts/src/lib.rs
@@ -145,7 +145,7 @@ impl Post {
 
 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)]
@@ -157,10 +157,10 @@ 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 {})
     }
@@ -170,14 +170,21 @@ impl State for Draft {
     }
 }
 
-struct PendingReview {}
+struct PendingReview {
+    acks: u32,
+}
+
 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> {
@@ -191,7 +198,7 @@ impl State for Published {
         Box::new(Self {})
     }
 
-    fn approve(&self) -> Box<dyn State> {
+    fn approve(&mut self) -> Box<dyn State> {
         Box::new(Published {})
     }
 
@@ -203,3 +210,46 @@ impl State for Published {
         &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}
+    }
+}