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Add shrink_to_fit #37

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Add shrink_to_fit #37

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bb4274d
Added shrink_to_fit
Kestrer Jun 13, 2020
18f8320
Test shrink_to_fit
Kestrer Jun 13, 2020
44da119
Fmt
Kestrer Jun 13, 2020
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105 changes: 66 additions & 39 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -300,19 +300,8 @@ impl<T> Arena<T> {
/// ```
pub fn clear(&mut self) {
self.items.clear();

let end = self.items.capacity();
self.items.extend((0..end).map(|i| {
if i == end - 1 {
Entry::Free { next_free: None }
} else {
Entry::Free {
next_free: Some(i + 1),
}
}
}));
self.free_list_head = Some(0);
self.len = 0;
self.reserve(self.items.capacity());
}

/// Attempts to insert `value` into the arena using existing capacity.
Expand Down Expand Up @@ -351,7 +340,7 @@ impl<T> Arena<T> {
value,
};
Ok(index)
},
}
}
}

Expand Down Expand Up @@ -392,7 +381,7 @@ impl<T> Arena<T> {
value: create(index),
};
Ok(index)
},
}
}
}

Expand All @@ -410,7 +399,7 @@ impl<T> Arena<T> {
generation: self.generation,
})
}
}
},
}
}

Expand Down Expand Up @@ -503,14 +492,19 @@ impl<T> Arena<T> {
Entry::Occupied { generation, .. } if i.generation == generation => {
let entry = mem::replace(
&mut self.items[i.index],
Entry::Free { next_free: self.free_list_head },
Entry::Free {
next_free: self.free_list_head,
},
);
self.generation += 1;
self.free_list_head = Some(i.index);
self.len -= 1;

match entry {
Entry::Occupied { generation: _, value } => Some(value),
Entry::Occupied {
generation: _,
value,
} => Some(value),
_ => unreachable!(),
}
}
Expand Down Expand Up @@ -598,10 +592,9 @@ impl<T> Arena<T> {
/// ```
pub fn get(&self, i: Index) -> Option<&T> {
match self.items.get(i.index) {
Some(Entry::Occupied {
generation,
value,
}) if *generation == i.generation => Some(value),
Some(Entry::Occupied { generation, value }) if *generation == i.generation => {
Some(value)
}
_ => None,
}
}
Expand All @@ -625,10 +618,9 @@ impl<T> Arena<T> {
/// ```
pub fn get_mut(&mut self, i: Index) -> Option<&mut T> {
match self.items.get_mut(i.index) {
Some(Entry::Occupied {
generation,
value,
}) if *generation == i.generation => Some(value),
Some(Entry::Occupied { generation, value }) if *generation == i.generation => {
Some(value)
}
_ => None,
}
}
Expand Down Expand Up @@ -690,18 +682,12 @@ impl<T> Arena<T> {
};

let item1 = match raw_item1 {
Entry::Occupied {
generation,
value,
} if *generation == i1.generation => Some(value),
Entry::Occupied { generation, value } if *generation == i1.generation => Some(value),
_ => None,
};

let item2 = match raw_item2 {
Entry::Occupied {
generation,
value,
} if *generation == i2.generation => Some(value),
Entry::Occupied { generation, value } if *generation == i2.generation => Some(value),
_ => None,
};

Expand Down Expand Up @@ -816,6 +802,41 @@ impl<T> Arena<T> {
self.free_list_head = Some(start);
}

/// Reduces allocated space to the minimum possible to fit all the elements in the arena.
///
/// # Examples
///
/// ```
/// use generational_arena::Arena;
///
/// let mut arena = Arena::new();
/// arena.extend([1, 2, 3, 4, 5].iter().copied());
/// assert!(arena.capacity() >= 5);
/// arena.shrink_to_fit();
/// assert_eq!(arena.capacity(), 5);
/// ```
pub fn shrink_to_fit(&mut self) {
self.items.truncate(
self.items
.iter()
.rposition(|entry| matches!(entry, Entry::Occupied { .. }))
.map(|n| n + 1)
.unwrap_or(0),
);
self.items.shrink_to_fit();

self.free_list_head = None;
for (i, item) in self.items.iter_mut().enumerate() {
match item {
Entry::Occupied { .. } => (),
Entry::Free { next_free } => {
*next_free = self.free_list_head;
self.free_list_head = Some(i);
}
}
}
}

/// Iterate over shared references to the elements in this arena.
///
/// Yields pairs of `(Index, &T)` items.
Expand Down Expand Up @@ -913,10 +934,13 @@ impl<T> Arena<T> {
/// You should use the `get` method instead most of the time.
pub fn get_unknown_gen(&self, i: usize) -> Option<(&T, Index)> {
match self.items.get(i) {
Some(Entry::Occupied {
generation,
Some(Entry::Occupied { generation, value }) => Some((
value,
}) => Some((value, Index { generation: *generation, index: i})),
Index {
generation: *generation,
index: i,
},
)),
_ => None,
}
}
Expand All @@ -933,10 +957,13 @@ impl<T> Arena<T> {
/// You should use the `get_mut` method instead most of the time.
pub fn get_unknown_gen_mut(&mut self, i: usize) -> Option<(&mut T, Index)> {
match self.items.get_mut(i) {
Some(Entry::Occupied {
generation,
Some(Entry::Occupied { generation, value }) => Some((
value,
}) => Some((value, Index { generation: *generation, index: i})),
Index {
generation: *generation,
index: i,
},
)),
_ => None,
}
}
Expand Down
2 changes: 1 addition & 1 deletion tests/quickchecks.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -177,7 +177,7 @@ quickcheck! {
}

arena.retain(|_, &mut b| b);

for live in live_indices.iter().cloned() {
assert!(arena.contains(live));
}
Expand Down
45 changes: 41 additions & 4 deletions tests/tests.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -134,11 +134,17 @@ fn get_unknown_gen() {
assert_eq!(id, idx);
assert_eq!(*el, 5);
} else {
panic!("element at index {} (without generation) should exist at this point", i);
panic!(
"element at index {} (without generation) should exist at this point",
i
);
}
arena.remove(idx);
if let Some((_, _)) = arena.get_unknown_gen(i) {
panic!("element at index {} (without generation) should not exist at this point", i);
panic!(
"element at index {} (without generation) should not exist at this point",
i
);
}
}

Expand All @@ -154,12 +160,18 @@ fn get_unknown_gen_mut() {
assert_eq!(*el, 5);
*el += 1;
} else {
panic!("element at index {} (without generation) should exist at this point", i);
panic!(
"element at index {} (without generation) should exist at this point",
i
);
}
assert_eq!(arena.get_mut(idx).cloned(), Some(6));
arena.remove(idx);
if let Some((_, _)) = arena.get_unknown_gen_mut(i) {
panic!("element at index {} (without generation) should not exist at this point", i);
panic!(
"element at index {} (without generation) should not exist at this point",
i
);
}
}

Expand Down Expand Up @@ -293,3 +305,28 @@ fn retain() {
assert_eq!(arena.len(), 1);
assert!(!arena.contains(index));
}

#[test]
fn shrink_to_fit() {
let mut arena = Arena::with_capacity(4);

arena.extend([1, 2, 3, 4].iter().copied());
let five = arena.insert(5);
assert_eq!(arena.capacity(), 8);

arena.shrink_to_fit();
assert_eq!(arena.len(), 5);
assert_eq!(arena.capacity(), 5);

arena.insert(6);
assert_eq!(arena.capacity(), 10);

arena.shrink_to_fit();
assert_eq!(arena.len(), 6);
assert_eq!(arena.capacity(), 6);

arena.remove(five);
arena.shrink_to_fit();
assert_eq!(arena.len(), 5);
assert_eq!(arena.capacity(), 6);
}