Module boa::class

Traits and structs for implementing native classes.

Native classes are implemented through the Class trait.

// This does not have to be an enum it can also be a struct.
#[derive(Debug, Trace, Finalize)]
enum Animal {
    Cat,
    Dog,
    Other,
}

impl Class for Animal {
    // we set the binging name of this function to be `"Animal"`.
    const NAME: &'static str = "Animal";

    // We set the length to `1` since we accept 1 arguments in the constructor.
    const LENGTH: usize = 1;

    // This is what is called when we do `new Animal()`
    fn constructor(_this: &Value, args: &[Value], context: &mut Context) -> Result<Self> {
        // This is equivalent to `String(arg)`.
        let kind = args.get(0).cloned().unwrap_or_default().to_string(context)?;

        let animal = match kind.as_str() {
            "cat" => Self::Cat,
            "dog" => Self::Dog,
            _ => Self::Other,
        };

        Ok(animal)
    }

    /// This is where the object is intitialized.
    fn init(class: &mut ClassBuilder) -> Result<()> {
        class.method("speak", 0, |this, _args, _ctx| {
            if let Some(object) = this.as_object() {
                if let Some(animal) = object.downcast_ref::<Animal>() {
                    match &*animal {
                        Self::Cat => println!("meow"),
                        Self::Dog => println!("woof"),
                        Self::Other => println!(r"¯\_(ツ)_/¯"),
                    }
                }
            }
            Ok(Value::undefined())
        });

        Ok(())
    }
}

Structs

ClassBuilder

Class builder which allows adding methods and static methods to the class.

Traits

Class	Native class.
ClassConstructor	This is a wrapper around Class::constructor that sets the internal data of a class.