RustBook 2nd edition 17.3 (2nd part implementation)

lib.rs

pub enum Content {
    Post(String),
    DraftPost(String),
    PendingReviewPost(String),
}

pub struct Post {
    approved: i32,
    content: Content,
}

impl Post {
    pub fn new() -> Post {
        Post { 
            approved: 0, 
            content: Content::DraftPost(String::new()) 
        }
    }

    pub fn content<'a>(&'a self) -> &'a str {
        match self.content {
            Content::Post(ref e) => e,
            _ => "",
        }
    }

    pub fn add_text(mut self, text: &str) -> Post{
        match self.content {
            Content::DraftPost(ref mut e) => {
                e.push_str(text);
            },
            _ => (),
        };
        self
    }

    pub fn request_review(self) -> Post {
        match self.content {
            Content::DraftPost(e) => Post { approved: 0, content: Content::PendingReviewPost(e) },
            _ => self,
        }
    }

    pub fn approve(mut self) -> Post {
        self.increase_approve();
        match self.content {
            Content::PendingReviewPost(ref e) if self.approved >= 2 => {
                Post { approved: 0, content: Content::Post(e.to_string())}
            },
            _ => self,
        }
    }

    fn increase_approve(&mut self) {
        match self.content {
            Content::PendingReviewPost(_) => self.approved += 1,
            _ => (),
        }
    }

    pub fn to_draft(self) -> Post {
        match self.content {
            Content::Post(e) => Post { 
                approved: 0,
                content: Content::DraftPost(e),
                ..self
            },
            _ => self,
        }
    }

    pub fn reject(self) -> Post {
        match self.content {
            Content::PendingReviewPost(e) => Post { approved: 0, content: Content::DraftPost(e)},
            _ => self,
        }
    }
}

main.rs

extern crate rust_learn;
use rust_learn::Post;

fn main() {
    let post = Post::new()
        .add_text("I ate a salad for lunch today")
        .request_review()
        .approve()
        .approve()
        .to_draft()
        .add_text("\nLalalala")
        .request_review()
        .approve()
        .reject()
        .request_review()
        .approve()
        .approve();

    assert_eq!("I ate a salad for lunch today\nLalalala", post.content());

}