blart 0.5.0

An implementation of an adaptive radix tree packaged as a BTreeMap replacement
Documentation 
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use core::fmt;

use super::{LeafNode, NodePtr};

type LeafPtr<K, V, const PREFIX_LEN: usize> = NodePtr<PREFIX_LEN, LeafNode<K, V, PREFIX_LEN>>;

struct RawIteratorInner<K, V, const PREFIX_LEN: usize> {
    start: LeafPtr<K, V, PREFIX_LEN>,
    end: LeafPtr<K, V, PREFIX_LEN>,
}

impl<K, V, const PREFIX_LEN: usize> Copy for RawIteratorInner<K, V, PREFIX_LEN> {}

impl<K, V, const PREFIX_LEN: usize> Clone for RawIteratorInner<K, V, PREFIX_LEN> {
    fn clone(&self) -> Self {
        *self
    }
}

impl<K, V, const PREFIX_LEN: usize> fmt::Debug for RawIteratorInner<K, V, PREFIX_LEN> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("RawIteratorInner")
            .field("start", &self.start)
            .field("end", &self.end)
            .finish()
    }
}

/// This struct represents a simple sort-iterator over leaves of a trie.
///
/// This struct does not actually implement the [`Iterator`] interface because
/// there are additional safety invariants on the [`next`][Self::next] and
/// [`next_back`][Self::next_back] functions.
pub struct RawIterator<K, V, const PREFIX_LEN: usize> {
    state: Option<RawIteratorInner<K, V, PREFIX_LEN>>,
}

impl<K, V, const PREFIX_LEN: usize> Copy for RawIterator<K, V, PREFIX_LEN> {}

impl<K, V, const PREFIX_LEN: usize> Clone for RawIterator<K, V, PREFIX_LEN> {
    fn clone(&self) -> Self {
        *self
    }
}

impl<K, V, const PREFIX_LEN: usize> fmt::Debug for RawIterator<K, V, PREFIX_LEN> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("RawIterator")
            .field("state", &self.state)
            .finish()
    }
}

impl<K, V, const PREFIX_LEN: usize> RawIterator<K, V, PREFIX_LEN> {
    /// Create a new [`RawIterator`] with the given starting and ending
    /// pointers.
    ///
    /// # Safety
    /// `start` must be before or equal to `end` in the linked list order.
    pub unsafe fn new(start: LeafPtr<K, V, PREFIX_LEN>, end: LeafPtr<K, V, PREFIX_LEN>) -> Self {
        Self {
            state: Some(RawIteratorInner { start, end }),
        }
    }

    pub fn empty() -> Self {
        Self { state: None }
    }

    /// If the iterator is not empty, return the next leaf pointer in the
    /// forward direction.
    ///
    /// If the iterator is empty, this function returns `None`.
    ///
    /// # Safety
    ///
    /// This function must not be called concurrently with any modification on
    /// the tree since it will use shared references on the leaves.
    pub unsafe fn next(&mut self) -> Option<LeafPtr<K, V, PREFIX_LEN>> {
        match &mut self.state {
            None => None,
            Some(RawIteratorInner { start, end }) => {
                let is_singleton = start == end;

                let next = *start;

                if is_singleton {
                    self.state = None;
                } else {
                    // SAFETY: Covered by function safety doc
                    let start_leaf = unsafe { start.as_ref() };

                    // PANIC SAFETY: We can unwrap here because `is_singleton` implies that `start`
                    // and `end` are different, which also implies that `start` does not point to
                    // the last/maximum leaf
                    *start = start_leaf.next.unwrap();
                }

                Some(next)
            },
        }
    }

    /// If the iterator is not empty, return the next leaf pointer in the
    /// backwards direction.
    ///
    /// If the iterator is empty, this function returns `None`.
    ///
    /// # Safety
    ///
    /// This function must not be called concurrently with any modification on
    /// the tree since it will use shared references on the leaves.
    pub unsafe fn next_back(&mut self) -> Option<LeafPtr<K, V, PREFIX_LEN>> {
        match &mut self.state {
            None => None,
            Some(RawIteratorInner { start, end }) => {
                let is_singleton = start == end;

                let next_back = *end;

                if is_singleton {
                    self.state = None;
                } else {
                    // SAFETY: Covered by function safety doc
                    let end_leaf = unsafe { end.as_ref() };

                    // PANIC SAFETY: We can unwrap here because `is_singleton` implies that `start`
                    // and `end` are different, which also implies that `end` does not point to
                    // the last/maximum leaf. The safety requirements of `RawIterator::new` also
                    // require that `start` is before or equal to `end` in the linked list order.
                    *end = end_leaf.previous.unwrap();
                }

                Some(next_back)
            },
        }
    }
}