84 lines
2.6 KiB
Rust
84 lines
2.6 KiB
Rust
pub(crate) trait PythonSubscript {
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type Item;
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fn python_subscript(&mut self, index: i64) -> Option<Self::Item>;
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}
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impl<I, T: DoubleEndedIterator<Item = I>> PythonSubscript for T {
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type Item = I;
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fn python_subscript(&mut self, index: i64) -> Option<I> {
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if index >= 0 {
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self.nth(usize::try_from(index).ok()?)
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} else {
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let nth_rev = usize::try_from(index.checked_neg()?).ok()?.checked_sub(1)?;
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self.rev().nth(nth_rev)
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}
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}
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}
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#[cfg(test)]
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#[allow(clippy::redundant_clone)]
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mod tests {
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use super::PythonSubscript;
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#[test]
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fn python_subscript_basic() {
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let iter = 'a'..='e';
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assert_eq!(iter.clone().python_subscript(0), Some('a'));
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assert_eq!(iter.clone().python_subscript(1), Some('b'));
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assert_eq!(iter.clone().python_subscript(4), Some('e'));
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assert_eq!(iter.clone().python_subscript(5), None);
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assert_eq!(iter.clone().python_subscript(-1), Some('e'));
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assert_eq!(iter.clone().python_subscript(-2), Some('d'));
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assert_eq!(iter.clone().python_subscript(-5), Some('a'));
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assert_eq!(iter.clone().python_subscript(-6), None);
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}
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#[test]
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fn python_subscript_empty() {
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let iter = 'a'..'a';
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assert_eq!(iter.clone().python_subscript(0), None);
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assert_eq!(iter.clone().python_subscript(1), None);
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assert_eq!(iter.clone().python_subscript(-1), None);
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}
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#[test]
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fn python_subscript_single_element() {
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let iter = 'a'..='a';
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assert_eq!(iter.clone().python_subscript(0), Some('a'));
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assert_eq!(iter.clone().python_subscript(1), None);
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assert_eq!(iter.clone().python_subscript(-1), Some('a'));
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assert_eq!(iter.clone().python_subscript(-2), None);
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}
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#[test]
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fn python_subscript_uses_full_index_range() {
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let iter = 0..=u64::MAX;
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assert_eq!(iter.clone().python_subscript(0), Some(0));
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assert_eq!(iter.clone().python_subscript(1), Some(1));
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assert_eq!(
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iter.clone().python_subscript(i64::MAX),
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Some(i64::MAX as u64)
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);
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assert_eq!(iter.clone().python_subscript(-1), Some(u64::MAX));
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assert_eq!(iter.clone().python_subscript(-2), Some(u64::MAX - 1));
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// i64::MIN is not representable as a positive number, so it is not
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// a valid index:
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assert_eq!(iter.clone().python_subscript(i64::MIN), None);
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// but i64::MIN +1 is:
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assert_eq!(
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iter.clone().python_subscript(i64::MIN + 1),
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Some(2u64.pow(63) + 1)
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);
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}
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}
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