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    use std::any::{Any, TypeId};
    use std::collections::HashMap;
    use std::fmt;
    use std::hash::{BuildHasherDefault, Hasher};

    struct IdHasher {
        id: u64,
    }

    impl Default for IdHasher {
        fn default() -> IdHasher {
            IdHasher { id: 0 }
        }
    }

    impl Hasher for IdHasher {
        fn write(&mut self, bytes: &[u8]) {
            for &x in bytes {
                self.id.wrapping_add(u64::from(x));
            }
        }

        fn write_u64(&mut self, u: u64) {
            self.id = u;
        }

        fn finish(&self) -> u64 {
            self.id
        }
    }

    type AnyMap = HashMap<TypeId, Box<Any>, BuildHasherDefault<IdHasher>>;

    /// A type map of request extensions.
    pub struct Extensions {
        map: AnyMap,
    }

    impl Extensions {
        /// Create an empty `Extensions`.
        #[inline]
        pub(crate) fn new() -> Extensions {
            Extensions {
                map: HashMap::default(),
            }
        }

        /// Insert a type into this `Extensions`.
        ///
        /// If a extension of this type already existed, it will
        /// be returned.
        pub fn insert<T: 'static>(&mut self, val: T) {
            self.map.insert(TypeId::of::<T>(), Box::new(val));
        }

        /// Get a reference to a type previously inserted on this `Extensions`.
        pub fn get<T: 'static>(&self) -> Option<&T> {
            self.map
                .get(&TypeId::of::<T>())
                .and_then(|boxed| (&**boxed as &(Any + 'static)).downcast_ref())
        }

        /// Get a mutable reference to a type previously inserted on this `Extensions`.
        pub fn get_mut<T: 'static>(&mut self) -> Option<&mut T> {
            self.map
                .get_mut(&TypeId::of::<T>())
                .and_then(|boxed| (&mut **boxed as &mut (Any + 'static)).downcast_mut())
        }

        /// Remove a type from this `Extensions`.
        ///
        /// If a extension of this type existed, it will be returned.
        pub fn remove<T: 'static>(&mut self) -> Option<T> {
            self.map.remove(&TypeId::of::<T>()).and_then(|boxed| {
                (boxed as Box<Any + 'static>)
                    .downcast()
                    .ok()
                    .map(|boxed| *boxed)
            })
        }

        /// Clear the `Extensions` of all inserted extensions.
        #[inline]
        pub fn clear(&mut self) {
            self.map.clear();
        }
    }

    impl fmt::Debug for Extensions {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            f.debug_struct("Extensions").finish()
        }
    }

    #[test]
    fn test_extensions() {
        #[derive(Debug, PartialEq)]
        struct MyType(i32);

        let mut extensions = Extensions::new();

        extensions.insert(5i32);
        extensions.insert(MyType(10));

        assert_eq!(extensions.get(), Some(&5i32));
        assert_eq!(extensions.get_mut(), Some(&mut 5i32));

        assert_eq!(extensions.remove::<i32>(), Some(5i32));
        assert!(extensions.get::<i32>().is_none());

        assert_eq!(extensions.get::<bool>(), None);
        assert_eq!(extensions.get(), Some(&MyType(10)));
    }

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