59 lines
1.4 KiB
Rust
59 lines
1.4 KiB
Rust
//! A double-ended iterator over entity references.
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//!
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//! When `std::iter::Step` is stablized, `Keys` could be implemented as a wrapper around
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//! `std::ops::Range`, but for now, we implment it manually.
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use std::marker::PhantomData;
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use EntityRef;
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/// Iterate over all keys in order.
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pub struct Keys<K: EntityRef> {
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pos: usize,
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rev_pos: usize,
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unused: PhantomData<K>,
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}
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impl<K: EntityRef> Keys<K> {
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/// Create a `Keys` iterator that visits `len` entities starting from 0.
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pub fn with_len(len: usize) -> Self {
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Self {
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pos: 0,
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rev_pos: len,
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unused: PhantomData,
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}
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}
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}
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impl<K: EntityRef> Iterator for Keys<K> {
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type Item = K;
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fn next(&mut self) -> Option<Self::Item> {
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if self.pos < self.rev_pos {
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let k = K::new(self.pos);
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self.pos += 1;
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Some(k)
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} else {
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None
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}
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}
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fn size_hint(&self) -> (usize, Option<usize>) {
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let size = self.rev_pos - self.pos;
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(size, Some(size))
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}
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}
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impl<K: EntityRef> DoubleEndedIterator for Keys<K> {
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fn next_back(&mut self) -> Option<Self::Item> {
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if self.rev_pos > self.pos {
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let k = K::new(self.rev_pos - 1);
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self.rev_pos -= 1;
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Some(k)
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} else {
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None
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}
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}
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}
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impl<K: EntityRef> ExactSizeIterator for Keys<K> {}
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