Tell me a story I could code #2

#story #code #rust #discuss

Originally post on my blog

Hello everyone! It's us again, Gaetan and Mathieu!
This is the second episode of Tell me a story I could code.
At our surprise, the concept worked more than we hope, and you, YES YOU, have been very prolific!

"What was proposed?"

In short, a movement, a dialog and the apparition of a dragon was proposed.
Here is how we have proceed.

First, we have now a dragon, which is still a character but different from a human.
Second, characters can speak to each other.
Third, characters can go to or come from location.

So, let's rename our Character structure to Human:

struct Human {
  name: String,
  money: i32,
}

and then create the Dragon struct:

struct Dragon {
  name: String,
}

Next step abstract the Character behaviour:

pub trait Character {
    fn new(name: &str) -> Self;

    fn says_to(&self, other: &Self, msg: &str);

    fn move_to(&self, location: &Self);

    fn get_name(&self) -> &str;

    fn run_away_from(&self, location: &Self);
}

But as it, the only Location a Charater can go to or run from is another Charater. So let say that we want Character able to do that with a Localisable struct.

pub trait Localizable {
    fn get_location(&self) -> String;
}

We can then adapt the Character struct like that to tell that some metho will use a type T that implements Localizable:

pub trait Character {
    fn new(name: &str) -> Self;

    fn says_to<T: Character>(&self, other: &T, msg: &str);

    fn move_to<T: Localizable>(&self, location: &T);

    fn get_name(&self) -> &str;

    fn run_away_from<T: Localizable>(&self, location: &T);
}

Then, we can implement those traits to Character

#[derive(Debug, Clone)]
pub struct Human {
    pub name: String,
    pub money: i32,
}

impl Human {
    pub fn find(&mut self, item: Item) {
        match item {
            Item::Money(amount) => {
                self.money += amount;
                println!("Oh {} penny! \" said {}.\"", amount, self.name);
            }
        }
    }
}

impl Character for Human {
    fn new(name: &str) -> Self {
        println!("There was a man named {}.", name);
        Human {
            name: name.to_owned(),
            money: 0,
        }
    }
    // Character needs to get back to another
    fn move_to<T: Localizable>(&self, location: &T) {
        println!("{} move to {}", self.name, location.get_location());
    }

    fn says_to<T: Character>(&self, other: &T, msg: &str) {
        println!("\"{}\" said {} to {}", msg, self.name, other.get_name());
    }

    fn get_name(&self) -> &str {
        self.name.as_str()
    }

    fn run_away_from<T: Localizable>(&self, location: &T) {
        println!("{} run away from {}", self.name, location.get_location());
    }
}

impl Localizable for Human {
    fn get_location(&self) -> String {
        self.name.clone()
    }
}

and for Dragon

#[derive(Debug, Clone)]
pub struct Dragon {
    pub name: String,
}

impl Dragon {
    pub fn fly_toward<T: Localizable>(&self, location: &T) {
        println!(
            "{} the dragon fly toward {}",
            self.name,
            location.get_location()
        );
    }
}

impl Localizable for Dragon {
    fn get_location(&self) -> String {
        format!("{} the dragon", self.name)
    }
}

impl Character for Dragon {
    fn new(name: &str) -> Self {
        println!("There was a dragon named {}.", name);
        Dragon {
            name: name.to_owned(),
        }
    }
    fn move_to<T: Localizable>(&self, location: &T) {
        println!("{} move to {}", self.name, location.get_location());
    }

    fn says_to<T: Character>(&self, other: &T, msg: &str) {
        println!("\"{}\" said {} to {}", msg, self.name, other.get_name());
    }

    fn get_name(&self) -> &str {
        &self.name
    }

    fn run_away_from<T: Localizable>(&self, location: &T) {
        println!(
            "How that, {} the dragon is running away from {}",
            self.name,
            location.get_location()
        );
    }
}

Note that we specified that only Human can find Item and that only Dragon can fly, so far.

Also note that the name inside Character was before a &'static str (meaning a String slice with a static lifetime) and have been change for a String. The reason for that it is easier to work with the String and do not require to care about the lifetime (the "scope" in which the variable lives) in case we have to return it in a fashion manner. Also, note that using static mean that the lifetime of the reference is the same as the application lifetime.

Now the output looks like:

Once upon a time...
There was a man named Bob.
Oh 1 penny! " said Bob."
There was a man named Joe.
Bob move to Joe
"Dude! Look what I found!" said Bob to Joe
"You should invest the penny in the Sheriff of Nottingham's Bank" said Joe to Bob
"But I already have invested money in the bank, I want to buy a horse!" said Bob to Joe
There was a dragon named Igorrr.
Igorrr the dragon fly toward Bob
Bob run away from Igorrr the dragon
"The shiny thing belongs to me" said Igorrr to Bob
"Never! Founders keepers, you Reptilebug!" said Bob to Igorrr

The full code is available here.