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use std::collections::HashSet;
use std::hash::Hash;
/// [`Iterator`] extension trait.
pub trait IteratorExt<Item>
where
Item: Eq + Hash,
{
/// Finds the first occurance of a duplicate item.
///
/// This function is short-circuiting. So it will immedietly return `Some` when
/// it comes across a item it has already seen.
///
/// The returned tuple contains the first item occurance & the second item occurance.
/// In that specific order.
///
/// Both items are returned in the case of the hash not being representative of the
/// whole item.
fn find_duplicate(self) -> Option<(Item, Item)>;
}
impl<Iter> IteratorExt<Iter::Item> for Iter
where
Iter: Iterator,
Iter::Item: Eq + Hash,
{
fn find_duplicate(self) -> Option<(Iter::Item, Iter::Item)>
{
let mut iterated_item_map = HashSet::<Iter::Item>::new();
for item in self {
if let Some(equal_item) = iterated_item_map.take(&item) {
return Some((item, equal_item));
}
iterated_item_map.insert(item);
}
None
}
}
#[cfg(test)]
mod tests
{
use super::*;
#[test]
fn can_find_dupe()
{
#[derive(Debug, PartialEq, Eq, Clone, Hash)]
struct Fruit
{
name: String,
}
assert_eq!(
[
Fruit {
name: "Apple".to_string(),
},
Fruit {
name: "Banana".to_string(),
},
Fruit {
name: "Apple".to_string(),
},
Fruit {
name: "Orange".to_string(),
},
]
.iter()
.find_duplicate(),
Some((
&Fruit {
name: "Apple".to_string()
},
&Fruit {
name: "Apple".to_string()
}
))
);
assert_eq!(
[
Fruit {
name: "Banana".to_string(),
},
Fruit {
name: "Apple".to_string(),
},
Fruit {
name: "Orange".to_string(),
},
]
.iter()
.find_duplicate(),
None
);
}
}
|
