// std::error

pub trait Error: Debug + Display {
    // existing API unchanged

    fn provide<'a>(&'a self, req: &mut Request<'a>) {}
}

pub struct Request<'a> { .. }

impl<'a> Request<'a> {
    pub fn provide_value<T>(&mut self, value: T) -> &mut Request<'a>
    where
        T: 'static;

    pub fn provide_value_with<T>(
        &mut self,
        fulfil: impl FnOnce() -> T,
    ) -> &mut Request<'a>
    where
        T: 'static;

    pub fn provide_ref<T>(&mut self, value: &'a T) -> &mut Request<'a>
    where
        T: 'static + ?Sized;

    pub fn provide_ref_with<T>(
        &mut self,
        fulfil: impl FnOnce() -> &'a T,
    ) -> &mut Request<'a>
    where
        T: 'static + ?Sized;

    pub fn would_be_satisfied_by_value_of<T>(&self) -> bool
    where
        T: 'static;

    pub fn would_be_satisfied_by_ref_of<T>(&self) -> bool
    where
        T: 'static + ?Sized;
}

pub fn request_ref<'a, T: ?Sized + 'static>(err: &'a (impl Error + ?Sized)) -> Option<&'a T>;

pub fn request_value<T: 'static>(err: &(impl Error + ?Sized)) -> Option<T>;