boreal thistle
#![feature(option_get_or_insert_default)]
use generic_array::{ArrayLength, GenericArray};
pub trait Prefix: Copy {
type Count: ArrayLength;
fn index(&self) -> usize;
}
/// Trie implementation
pub struct PrefixTree<T: Prefix> {
children: GenericArray<Option<Box<Self>>, T::Count>,
end: bool,
}
struct WalkMut<'a, T: Prefix, I: Iterator<Item = usize>> {
node: &'a mut PrefixTree<T>,
indices: I,
}
impl<'a, T: Prefix, I: Iterator<Item = usize>> Iterator for WalkMut<'a, T, I> {
type Item = Option<&'a mut PrefixTree<T>>;
fn next(&mut self) -> Option<Self::Item> {
let index = self.indices.next()?;
if let Some(child) = self.node.children[index].as_deref_mut() {
self.node = child;
Some(Some(self.node))
} else {
Some(None)
}
}
}
impl<T: Prefix> PrefixTree<T> {
#[must_use]
fn walk_mut<I: IntoIterator<Item = usize>>(&mut self, indices: I) -> WalkMut<'_, T, I::IntoIter> {
WalkMut {
node: self,
indices: indices.into_iter(),
}
}
}
I'm writing a prefix tree and currently implementing a walk iterator to allow walking the tree via indices. The non-mutable Walk iterator works however the mutable WalkMut iterator fails to compile due to compiler errors. Here's all the code: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=6ec2b843e130b627c6dca20ba5b1ec28
error: lifetime may not live long enough
--> src/lib.rs:60:13
|
44 | impl<'a, T: Prefix, I: Iterator<Item = usize>> Iterator for WalkMut<'a, T, I> {
| -- lifetime `'a` defined here
...
54 | fn next(&mut self) -> Option<Self::Item> {
| - let's call the lifetime of this reference `'1`
...
60 | Some(Some(self.node))
| ^^^^^^^^^^^^^^^^^^^^^ method was supposed to return data with lifetime `'a` but it is returning data with lifetime `'1`
earnest panther