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use handle::{Skip, Take}; /// Allows borrowing a value of type `T` from the implementing type. This can be used to constrain /// a `Handle` argument to ensure it can be used with the corresponding `BorrowBag`. /// /// # Examples /// /// ```rust /// # use borrow_bag::*; /// # /// fn borrow_from<V, T, N>(bag: &BorrowBag<V>, handle: Handle<T, N>) -> &T /// where V: Lookup<T, N> /// { /// bag.borrow(handle) /// } /// ``` pub trait Lookup<T, N> { /// Borrows the value of type `T`. Internal API and not for public use. #[doc(hidden)] fn get_from(&self) -> &T; } #[doc(hidden)] impl<T, U, V, N> Lookup<T, (Skip, N)> for (U, V) where V: Lookup<T, N> { fn get_from(&self) -> &T { self.1.get_from() } } #[doc(hidden)] impl<T, V> Lookup<T, Take> for (T, V) { fn get_from(&self) -> &T { &self.0 } }