Trait UserDataType
box2d_rs::b2_settings
pub trait UserDataType: Default + Clone + 'static { type Fixture: Default + Clone + Debug; type Body: Default + Clone + PartialEq + Debug; type Joint: Default + Clone + Debug; }
type Fixture: Default + Clone + Debug
type Body: Default + Clone + PartialEq + Debug
type Joint: Default + Clone + Debug