use std::marker::PhantomData;

trait Cons {
    const PI: f32;
}

struct Vague;
impl Cons for Vague {
    const PI: f32 = 3.14;
}

struct Outer<T: Cons>(PhantomData<T>);

impl<T: Cons> Outer<T> {
    fn pi(&self) -> f32 {
        T::PI
    }
}

fn main() {
    let x = Outer::<Vague>(PhantomData);
    println!("{}", x.pi());
}