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    use std::prelude::v1::*;

    use std::any::TypeId;
    use std::cell::RefCell;
    use std::hash::{BuildHasherDefault, Hasher};
    use std::collections::HashMap;

    use task_impl::with;

    /// A macro to create a `static` of type `LocalKey`
    ///
    /// This macro is intentionally similar to the `thread_local!`, and creates a
    /// `static` which has a `with` method to access the data on a task.
    ///
    /// The data associated with each task local is per-task, so different tasks
    /// will contain different values.
    #[macro_export]
    macro_rules! task_local {
        (static $NAME:ident: $t:ty = $e:expr) => (
            static $NAME: $crate::task::LocalKey<$t> = {
                fn __init() -> $t { $e }
                fn __key() -> ::std::any::TypeId {
                    struct __A;
                    ::std::any::TypeId::of::<__A>()
                }
                $crate::task::LocalKey {
                    __init: __init,
                    __key: __key,
                }
            };
        )
    }

    pub type LocalMap = RefCell<HashMap<TypeId,
                                        Box<Opaque>,
                                        BuildHasherDefault<IdHasher>>>;

    pub fn local_map() -> LocalMap {
        RefCell::new(HashMap::default())
    }

    pub trait Opaque: Send {}
    impl<T: Send> Opaque for T {}

    /// A key for task-local data stored in a future's task.
    ///
    /// This type is generated by the `task_local!` macro and performs very
    /// similarly to the `thread_local!` macro and `std::thread::LocalKey` types.
    /// Data associated with a `LocalKey<T>` is stored inside of a future's task,
    /// and the data is destroyed when the future is completed and the task is
    /// destroyed.
    ///
    /// Task-local data can migrate between threads and hence requires a `Send`
    /// bound. Additionally, task-local data also requires the `'static` bound to
    /// ensure it lives long enough. When a key is accessed for the first time the
    /// task's data is initialized with the provided initialization expression to
    /// the macro.
    #[derive(Debug)]
    pub struct LocalKey<T> {
        // "private" fields which have to be public to get around macro hygiene, not
        // included in the stability story for this type. Can change at any time.
        #[doc(hidden)]
        pub __key: fn() -> TypeId,
        #[doc(hidden)]
        pub __init: fn() -> T,
    }

    pub struct IdHasher {
        id: u64,
    }

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

    impl Hasher for IdHasher {
        fn write(&mut self, _bytes: &[u8]) {
            // TODO: need to do something sensible
            panic!("can only hash u64");
        }

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

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

    impl<T: Send + 'static> LocalKey<T> {
        /// Access this task-local key, running the provided closure with a
        /// reference to the value.
        ///
        /// This function will access this task-local key to retrieve the data
        /// associated with the current task and this key. If this is the first time
        /// this key has been accessed on this task, then the key will be
        /// initialized with the initialization expression provided at the time the
        /// `task_local!` macro was called.
        ///
        /// The provided closure will be provided a shared reference to the
        /// underlying data associated with this task-local-key. The data itself is
        /// stored inside of the current task.
        ///
        /// # Panics
        ///
        /// This function can possibly panic for a number of reasons:
        ///
        /// * If there is not a current task.
        /// * If the initialization expression is run and it panics
        /// * If the closure provided panics
        pub fn with<F, R>(&'static self, f: F) -> R
            where F: FnOnce(&T) -> R
        {
            let key = (self.__key)();
            with(|task| {
                let raw_pointer = {
                    let mut data = task.map.borrow_mut();
                    let entry = data.entry(key).or_insert_with(|| {
                        Box::new((self.__init)())
                    });
                    &**entry as *const Opaque as *const T
                };
                unsafe {
                    f(&*raw_pointer)
                }
            })
        }
    }

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