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use std::iter::FusedIterator; use crate::DftPre; /// Produces all paths using /// [Depth-First Traversal] (in Pre-Order). /// /// [Depth-First Traversal]: https://en.wikipedia.org/wiki/Tree_traversal /// /// # Cycles /// /// `DftPaths` does not handle cycles. If any /// cycles are present, then `DftPaths` will /// result in an infinite (never ending) /// [`Iterator`]. /// /// [`Iterator`]: https://doc.rust-lang.org/stable/std/iter/trait.Iterator.html /// /// # Example /// /// ``` /// use traversal::DftPaths; /// /// struct Node(&'static str, &'static [Node]); /// /// let tree = Node("A", &[ /// Node("B", &[ /// Node("C", &[]), /// Node("D", &[]) /// ]), /// Node("E", &[ /// Node("F", &[]), /// Node("G", &[]) /// ]), /// ]); /// /// // `&tree` represents the root `Node`. /// // The `FnMut(&Node) -> Iterator<Item = &Node>` returns /// // an `Iterator` to get the child `Node`s. /// let iter = DftPaths::new(&tree, |node| node.1.iter()); /// /// // Map `Iterator<Item = Vec<&Node>>` into `Iterator<Item = Vec<&str>>` /// let mut iter = iter.map(|path| path.iter().map(|node| node.0).collect::<Vec<_>>()); /// /// assert_eq!(iter.next(), Some(vec!["A", "B"])); /// assert_eq!(iter.next(), Some(vec!["A", "B", "C"])); /// assert_eq!(iter.next(), Some(vec!["A", "B", "D"])); /// assert_eq!(iter.next(), Some(vec!["A", "E"])); /// assert_eq!(iter.next(), Some(vec!["A", "E", "F"])); /// assert_eq!(iter.next(), Some(vec!["A", "E", "G"])); /// assert_eq!(iter.next(), None); /// ``` #[allow(missing_debug_implementations)] #[derive(Clone)] pub struct DftPaths<'a, T, F, I> where T: ?Sized, F: FnMut(&'a T) -> I, I: Iterator<Item = &'a T>, { path: Vec<&'a T>, iter: DftPre<'a, T, F, I>, } impl<'a, T, F, I> DftPaths<'a, T, F, I> where T: ?Sized, F: FnMut(&'a T) -> I, I: Iterator<Item = &'a T>, { /// Creates a `DftPaths`, where `root` is the /// starting `Node`. /// /// The `iter_children` [`FnMut`] is (lazily) called /// for each `Node` as needed, where the /// returned [`Iterator`] produces the child /// `Node`s for the given `Node`. /// /// [`Iterator`]: https://doc.rust-lang.org/stable/std/iter/trait.Iterator.html /// /// *[See `DftPaths` for more information.][`DftPaths`]* /// /// [`DftPaths`]: struct.DftPaths.html /// /// # "`FnOnce`" /// /// The [`FnMut`] is a [`FnOnce`] from the point-of-view of /// a `Node`, as `iter_children` is at most called once for /// each individual `Node`. /// /// [`FnMut`]: https://doc.rust-lang.org/std/ops/trait.FnMut.html /// [`FnOnce`]: https://doc.rust-lang.org/std/ops/trait.FnOnce.html /// /// # `FusedIterator` /// /// While `DftPaths` does not require [`FusedIterator`], /// it assumes that no `Node`s are produced after /// a `None`. /// /// [`FusedIterator`]: https://doc.rust-lang.org/stable/std/iter/trait.FusedIterator.html #[inline] pub fn new(root: &'a T, iter_children: F) -> Self { let mut iter = DftPre::new(root, iter_children); // Safe to use `unwrap` as `DftPre` with `root` at least produces `root` Self { path: vec![iter.next().unwrap().1], iter, } } } impl<'a, T, F, I> Iterator for DftPaths<'a, T, F, I> where T: ?Sized, F: FnMut(&'a T) -> I, I: Iterator<Item = &'a T>, { type Item = Vec<&'a T>; #[inline] fn next(&mut self) -> Option<Self::Item> { if let Some((depth, node)) = self.iter.next() { self.path.truncate(depth); self.path.push(node); Some(self.path.clone()) } else { None } } } impl<'a, T, F, I> FusedIterator for DftPaths<'a, T, F, I> where T: ?Sized, F: FnMut(&'a T) -> I, I: Iterator<Item = &'a T>, { } #[cfg(test)] mod tests { use super::*; struct Node(&'static str, &'static [Node]); #[test] fn dft_paths() { #[rustfmt::skip] let tree = Node("A", &[ Node("B", &[ Node("C", &[]), Node("D", &[ Node("E", &[]) ])]), Node("F", &[ Node("G", &[ Node("H", &[]) ]), Node("I", &[])]), ]); let iter = DftPaths::new(&tree, |node| node.1.iter()); let mut iter = iter.map(|path| path.iter().map(|node| node.0).collect::<Vec<_>>()); assert_eq!(iter.next(), Some(vec!["A", "B"])); assert_eq!(iter.next(), Some(vec!["A", "B", "C"])); assert_eq!(iter.next(), Some(vec!["A", "B", "D"])); assert_eq!(iter.next(), Some(vec!["A", "B", "D", "E"])); assert_eq!(iter.next(), Some(vec!["A", "F"])); assert_eq!(iter.next(), Some(vec!["A", "F", "G"])); assert_eq!(iter.next(), Some(vec!["A", "F", "G", "H"])); assert_eq!(iter.next(), Some(vec!["A", "F", "I"])); assert_eq!(iter.next(), None); } }