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    use super::plumbing::*;
    use super::*;

    use std::fmt::{self, Debug};

    /// `FilterMap` creates an iterator that uses `filter_op` to both filter and map elements.
    /// This struct is created by the [`filter_map()`] method on [`ParallelIterator`].
    ///
    /// [`filter_map()`]: trait.ParallelIterator.html#method.filter_map
    /// [`ParallelIterator`]: trait.ParallelIterator.html
    #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
    #[derive(Clone)]
    pub struct FilterMap<I: ParallelIterator, P> {
        base: I,
        filter_op: P,
    }

    impl<I: ParallelIterator + Debug, P> Debug for FilterMap<I, P> {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            f.debug_struct("FilterMap")
                .field("base", &self.base)
                .finish()
        }
    }

    impl<I: ParallelIterator, P> FilterMap<I, P> {
        /// Create a new `FilterMap` iterator.
        pub(super) fn new(base: I, filter_op: P) -> Self {
            FilterMap { base, filter_op }
        }
    }

    impl<I, P, R> ParallelIterator for FilterMap<I, P>
    where
        I: ParallelIterator,
        P: Fn(I::Item) -> Option<R> + Sync + Send,
        R: Send,
    {
        type Item = R;

        fn drive_unindexed<C>(self, consumer: C) -> C::Result
        where
            C: UnindexedConsumer<Self::Item>,
        {
            let consumer = FilterMapConsumer::new(consumer, &self.filter_op);
            self.base.drive_unindexed(consumer)
        }
    }

    /// ////////////////////////////////////////////////////////////////////////
    /// Consumer implementation

    struct FilterMapConsumer<'p, C, P: 'p> {
        base: C,
        filter_op: &'p P,
    }

    impl<'p, C, P: 'p> FilterMapConsumer<'p, C, P> {
        fn new(base: C, filter_op: &'p P) -> Self {
            FilterMapConsumer { base, filter_op }
        }
    }

    impl<'p, T, U, C, P> Consumer<T> for FilterMapConsumer<'p, C, P>
    where
        C: Consumer<U>,
        P: Fn(T) -> Option<U> + Sync + 'p,
    {
        type Folder = FilterMapFolder<'p, C::Folder, P>;
        type Reducer = C::Reducer;
        type Result = C::Result;

        fn split_at(self, index: usize) -> (Self, Self, Self::Reducer) {
            let (left, right, reducer) = self.base.split_at(index);
            (
                FilterMapConsumer::new(left, self.filter_op),
                FilterMapConsumer::new(right, self.filter_op),
                reducer,
            )
        }

        fn into_folder(self) -> Self::Folder {
            let base = self.base.into_folder();
            FilterMapFolder {
                base,
                filter_op: self.filter_op,
            }
        }

        fn full(&self) -> bool {
            self.base.full()
        }
    }

    impl<'p, T, U, C, P> UnindexedConsumer<T> for FilterMapConsumer<'p, C, P>
    where
        C: UnindexedConsumer<U>,
        P: Fn(T) -> Option<U> + Sync + 'p,
    {
        fn split_off_left(&self) -> Self {
            FilterMapConsumer::new(self.base.split_off_left(), &self.filter_op)
        }

        fn to_reducer(&self) -> Self::Reducer {
            self.base.to_reducer()
        }
    }

    struct FilterMapFolder<'p, C, P: 'p> {
        base: C,
        filter_op: &'p P,
    }

    impl<'p, T, U, C, P> Folder<T> for FilterMapFolder<'p, C, P>
    where
        C: Folder<U>,
        P: Fn(T) -> Option<U> + Sync + 'p,
    {
        type Result = C::Result;

        fn consume(self, item: T) -> Self {
            let filter_op = self.filter_op;
            if let Some(mapped_item) = filter_op(item) {
                let base = self.base.consume(mapped_item);
                FilterMapFolder { base, filter_op }
            } else {
                self
            }
        }

        // This cannot easily specialize `consume_iter` to be better than
        // the default, because that requires checking `self.base.full()`
        // during a call to `self.base.consume_iter()`. (#632)

        fn complete(self) -> C::Result {
            self.base.complete()
        }

        fn full(&self) -> bool {
            self.base.full()
        }
    }

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