4 files changed, 68 insertions, 0 deletions
diff --git a/src/doc/book/listings/ch17-oop/listing-17-21/Cargo.lock b/src/doc/book/listings/ch17-oop/listing-17-21/Cargo.lock
new file mode 100644
index 000000000..b6f4232c6
--- /dev/null
+++ b/src/doc/book/listings/ch17-oop/listing-17-21/Cargo.lock
@@ -0,0 +1,6 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "blog"
+version = "0.1.0"
+
diff --git a/src/doc/book/listings/ch17-oop/listing-17-21/Cargo.toml b/src/doc/book/listings/ch17-oop/listing-17-21/Cargo.toml
new file mode 100644
index 000000000..1619af5c6
--- /dev/null
+++ b/src/doc/book/listings/ch17-oop/listing-17-21/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "blog"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
diff --git a/src/doc/book/listings/ch17-oop/listing-17-21/src/lib.rs b/src/doc/book/listings/ch17-oop/listing-17-21/src/lib.rs
new file mode 100644
index 000000000..38500a651
--- /dev/null
+++ b/src/doc/book/listings/ch17-oop/listing-17-21/src/lib.rs
@@ -0,0 +1,43 @@
+pub struct Post {
+    content: String,
+}
+
+pub struct DraftPost {
+    content: String,
+}
+
+impl Post {
+    pub fn new() -> DraftPost {
+        DraftPost {
+            content: String::new(),
+        }
+    }
+
+    pub fn content(&self) -> &str {
+        &self.content
+    }
+}
+
+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,
+        }
+    }
+}
diff --git a/src/doc/book/listings/ch17-oop/listing-17-21/src/main.rs b/src/doc/book/listings/ch17-oop/listing-17-21/src/main.rs
new file mode 100644
index 000000000..720c55e6a
--- /dev/null
+++ b/src/doc/book/listings/ch17-oop/listing-17-21/src/main.rs
@@ -0,0 +1,13 @@
+use blog::Post;
+
+fn main() {
+    let mut post = 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());
+}