`pub struct IndexSet<T, S = RandomState> { /* private fields */ }`

## Expand description

A hash set where the iteration order of the values is independent of their hash values.

The interface is closely compatible with the standard `HashSet`

, but also
has additional features.

## Order

The values have a consistent order that is determined by the sequence of insertion and removal calls on the set. The order does not depend on the values or the hash function at all. Note that insertion order and value are not affected if a re-insertion is attempted once an element is already present.

All iterators traverse the set *in order*. Set operation iterators like
`union`

produce a concatenated order, as do their matching “bitwise”
operators. See their documentation for specifics.

The insertion order is preserved, with **notable exceptions** like the
`.remove()`

or `.swap_remove()`

methods. Methods such as `.sort_by()`

of
course result in a new order, depending on the sorting order.

## Indices

The values are indexed in a compact range without holes in the range
`0..self.len()`

. For example, the method `.get_full`

looks up the index for
a value, and the method `.get_index`

looks up the value by index.

## Examples

```
use indexmap::IndexSet;
// Collects which letters appear in a sentence.
let letters: IndexSet<_> = "a short treatise on fungi".chars().collect();
assert!(letters.contains(&'s'));
assert!(letters.contains(&'t'));
assert!(letters.contains(&'u'));
assert!(!letters.contains(&'y'));
```

## Implementations

source### impl<T> IndexSet<T>

### impl<T> IndexSet<T>

source#### pub fn with_capacity(n: usize) -> Self

#### pub fn with_capacity(n: usize) -> Self

Create a new set with capacity for `n`

elements.
(Does not allocate if `n`

is zero.)

Computes in **O(n)** time.

source### impl<T, S> IndexSet<T, S>

### impl<T, S> IndexSet<T, S>

source#### pub fn with_capacity_and_hasher(n: usize, hash_builder: S) -> Selfwhere

S: BuildHasher,

#### pub fn with_capacity_and_hasher(n: usize, hash_builder: S) -> Selfwhere

S: BuildHasher,

Create a new set with capacity for `n`

elements.
(Does not allocate if `n`

is zero.)

Computes in **O(n)** time.

source#### pub fn is_empty(&self) -> bool

#### pub fn is_empty(&self) -> bool

Returns true if the set contains no elements.

Computes in **O(1)** time.

source#### pub fn with_hasher(hash_builder: S) -> Selfwhere

S: BuildHasher,

#### pub fn with_hasher(hash_builder: S) -> Selfwhere

S: BuildHasher,

Create a new set with `hash_builder`

source#### pub fn hasher(&self) -> &Swhere

S: BuildHasher,

#### pub fn hasher(&self) -> &Swhere

S: BuildHasher,

Return a reference to the set’s `BuildHasher`

.

source### impl<T, S> IndexSet<T, S>where

T: Hash + Eq,

S: BuildHasher,

### impl<T, S> IndexSet<T, S>where

T: Hash + Eq,

S: BuildHasher,

source#### pub fn clear(&mut self)

#### pub fn clear(&mut self)

Remove all elements in the set, while preserving its capacity.

Computes in **O(n)** time.

source#### pub fn insert(&mut self, value: T) -> bool

#### pub fn insert(&mut self, value: T) -> bool

Insert the value into the set.

If an equivalent item already exists in the set, it returns
`false`

leaving the original value in the set and without
altering its insertion order. Otherwise, it inserts the new
item and returns `true`

.

Computes in **O(1)** time (amortized average).

source#### pub fn insert_full(&mut self, value: T) -> (usize, bool)

#### pub fn insert_full(&mut self, value: T) -> (usize, bool)

Insert the value into the set, and get its index.

If an equivalent item already exists in the set, it returns
the index of the existing item and `false`

, leaving the
original value in the set and without altering its insertion
order. Otherwise, it inserts the new item and returns the index
of the inserted item and `true`

.

Computes in **O(1)** time (amortized average).

source#### pub fn iter(&self) -> Iter<'_, T>ⓘNotable traits for Iter<'a, T>`impl<'a, T> Iterator for Iter<'a, T> type Item = &'a T;`

#### pub fn iter(&self) -> Iter<'_, T>ⓘNotable traits for Iter<'a, T>`impl<'a, T> Iterator for Iter<'a, T> type Item = &'a T;`

Return an iterator over the values of the set, in their order

source#### pub fn difference<'a, S2>(

&'a self,

other: &'a IndexSet<T, S2>

) -> Difference<'a, T, S2>ⓘNotable traits for Difference<'a, T, S>`impl<'a, T, S> Iterator for Difference<'a, T, S>where`

T: Eq + Hash,

S: BuildHasher, type Item = &'a T;

where

S2: BuildHasher,

#### pub fn difference<'a, S2>(

&'a self,

other: &'a IndexSet<T, S2>

) -> Difference<'a, T, S2>ⓘNotable traits for Difference<'a, T, S>`impl<'a, T, S> Iterator for Difference<'a, T, S>where`

T: Eq + Hash,

S: BuildHasher, type Item = &'a T;

where

S2: BuildHasher,

T: Eq + Hash,

S: BuildHasher, type Item = &'a T;

Return an iterator over the values that are in `self`

but not `other`

.

Values are produced in the same order that they appear in `self`

.

source#### pub fn symmetric_difference<'a, S2>(

&'a self,

other: &'a IndexSet<T, S2>

) -> SymmetricDifference<'a, T, S, S2>ⓘNotable traits for SymmetricDifference<'a, T, S1, S2>`impl<'a, T, S1, S2> Iterator for SymmetricDifference<'a, T, S1, S2>where`

T: Eq + Hash,

S1: BuildHasher,

S2: BuildHasher, type Item = &'a T;

where

S2: BuildHasher,

#### pub fn symmetric_difference<'a, S2>(

&'a self,

other: &'a IndexSet<T, S2>

) -> SymmetricDifference<'a, T, S, S2>ⓘNotable traits for SymmetricDifference<'a, T, S1, S2>`impl<'a, T, S1, S2> Iterator for SymmetricDifference<'a, T, S1, S2>where`

T: Eq + Hash,

S1: BuildHasher,

S2: BuildHasher, type Item = &'a T;

where

S2: BuildHasher,

T: Eq + Hash,

S1: BuildHasher,

S2: BuildHasher, type Item = &'a T;

Return an iterator over the values that are in `self`

or `other`

,
but not in both.

Values from `self`

are produced in their original order, followed by
values from `other`

in their original order.

source#### pub fn intersection<'a, S2>(

&'a self,

other: &'a IndexSet<T, S2>

) -> Intersection<'a, T, S2>ⓘNotable traits for Intersection<'a, T, S>`impl<'a, T, S> Iterator for Intersection<'a, T, S>where`

T: Eq + Hash,

S: BuildHasher, type Item = &'a T;

where

S2: BuildHasher,

#### pub fn intersection<'a, S2>(

&'a self,

other: &'a IndexSet<T, S2>

) -> Intersection<'a, T, S2>ⓘNotable traits for Intersection<'a, T, S>`impl<'a, T, S> Iterator for Intersection<'a, T, S>where`

T: Eq + Hash,

S: BuildHasher, type Item = &'a T;

where

S2: BuildHasher,

T: Eq + Hash,

S: BuildHasher, type Item = &'a T;

Return an iterator over the values that are in both `self`

and `other`

.

Values are produced in the same order that they appear in `self`

.

source#### pub fn union<'a, S2>(&'a self, other: &'a IndexSet<T, S2>) -> Union<'a, T, S>ⓘNotable traits for Union<'a, T, S>`impl<'a, T, S> Iterator for Union<'a, T, S>where`

T: Eq + Hash,

S: BuildHasher, type Item = &'a T;

where

S2: BuildHasher,

#### pub fn union<'a, S2>(&'a self, other: &'a IndexSet<T, S2>) -> Union<'a, T, S>ⓘNotable traits for Union<'a, T, S>`impl<'a, T, S> Iterator for Union<'a, T, S>where`

T: Eq + Hash,

S: BuildHasher, type Item = &'a T;

where

S2: BuildHasher,

T: Eq + Hash,

S: BuildHasher, type Item = &'a T;

Return an iterator over all values that are in `self`

or `other`

.

Values from `self`

are produced in their original order, followed by
values that are unique to `other`

in their original order.

source#### pub fn contains<Q: ?Sized>(&self, value: &Q) -> boolwhere

Q: Hash + Equivalent<T>,

#### pub fn contains<Q: ?Sized>(&self, value: &Q) -> boolwhere

Q: Hash + Equivalent<T>,

Return `true`

if an equivalent to `value`

exists in the set.

Computes in **O(1)** time (average).

source#### pub fn get<Q: ?Sized>(&self, value: &Q) -> Option<&T>where

Q: Hash + Equivalent<T>,

#### pub fn get<Q: ?Sized>(&self, value: &Q) -> Option<&T>where

Q: Hash + Equivalent<T>,

Return a reference to the value stored in the set, if it is present,
else `None`

.

Computes in **O(1)** time (average).

source#### pub fn get_full<Q: ?Sized>(&self, value: &Q) -> Option<(usize, &T)>where

Q: Hash + Equivalent<T>,

#### pub fn get_full<Q: ?Sized>(&self, value: &Q) -> Option<(usize, &T)>where

Q: Hash + Equivalent<T>,

Return item index and value

source#### pub fn replace(&mut self, value: T) -> Option<T>

#### pub fn replace(&mut self, value: T) -> Option<T>

Adds a value to the set, replacing the existing value, if any, that is equal to the given one. Returns the replaced value.

Computes in **O(1)** time (average).

source#### pub fn remove<Q: ?Sized>(&mut self, value: &Q) -> boolwhere

Q: Hash + Equivalent<T>,

#### pub fn remove<Q: ?Sized>(&mut self, value: &Q) -> boolwhere

Q: Hash + Equivalent<T>,

FIXME Same as .swap_remove

Computes in **O(1)** time (average).

source#### pub fn swap_remove<Q: ?Sized>(&mut self, value: &Q) -> boolwhere

Q: Hash + Equivalent<T>,

#### pub fn swap_remove<Q: ?Sized>(&mut self, value: &Q) -> boolwhere

Q: Hash + Equivalent<T>,

Remove the value from the set, and return `true`

if it was present.

Like `Vec::swap_remove`

, the value is removed by swapping it with the
last element of the set and popping it off. **This perturbs
the postion of what used to be the last element!**

Return `false`

if `value`

was not in the set.

Computes in **O(1)** time (average).

source#### pub fn take<Q: ?Sized>(&mut self, value: &Q) -> Option<T>where

Q: Hash + Equivalent<T>,

#### pub fn take<Q: ?Sized>(&mut self, value: &Q) -> Option<T>where

Q: Hash + Equivalent<T>,

FIXME Same as .swap_take

Computes in **O(1)** time (average).

source#### pub fn swap_take<Q: ?Sized>(&mut self, value: &Q) -> Option<T>where

Q: Hash + Equivalent<T>,

#### pub fn swap_take<Q: ?Sized>(&mut self, value: &Q) -> Option<T>where

Q: Hash + Equivalent<T>,

Removes and returns the value in the set, if any, that is equal to the given one.

Like `Vec::swap_remove`

, the value is removed by swapping it with the
last element of the set and popping it off. **This perturbs
the postion of what used to be the last element!**

Return `None`

if `value`

was not in the set.

Computes in **O(1)** time (average).

source#### pub fn swap_remove_full<Q: ?Sized>(&mut self, value: &Q) -> Option<(usize, T)>where

Q: Hash + Equivalent<T>,

#### pub fn swap_remove_full<Q: ?Sized>(&mut self, value: &Q) -> Option<(usize, T)>where

Q: Hash + Equivalent<T>,

Remove the value from the set return it and the index it had.

Like `Vec::swap_remove`

, the value is removed by swapping it with the
last element of the set and popping it off. **This perturbs
the postion of what used to be the last element!**

Return `None`

if `value`

was not in the set.

source#### pub fn retain<F>(&mut self, keep: F)where

F: FnMut(&T) -> bool,

#### pub fn retain<F>(&mut self, keep: F)where

F: FnMut(&T) -> bool,

Scan through each value in the set and keep those where the
closure `keep`

returns `true`

.

The elements are visited in order, and remaining elements keep their order.

Computes in **O(n)** time (average).

source#### pub fn sort(&mut self)where

T: Ord,

#### pub fn sort(&mut self)where

T: Ord,

Sort the set’s values by their default ordering.

See `sort_by`

for details.

source#### pub fn sort_by<F>(&mut self, compare: F)where

F: FnMut(&T, &T) -> Ordering,

#### pub fn sort_by<F>(&mut self, compare: F)where

F: FnMut(&T, &T) -> Ordering,

Sort the set’s values in place using the comparison function `compare`

.

Computes in **O(n log n)** time and **O(n)** space. The sort is stable.

source### impl<T, S> IndexSet<T, S>

### impl<T, S> IndexSet<T, S>

source#### pub fn get_index(&self, index: usize) -> Option<&T>

#### pub fn get_index(&self, index: usize) -> Option<&T>

Get a value by index

Valid indices are *0 <= index < self.len()*

Computes in **O(1)** time.

source#### pub fn swap_remove_index(&mut self, index: usize) -> Option<T>

#### pub fn swap_remove_index(&mut self, index: usize) -> Option<T>

Remove the key-value pair by index

Valid indices are *0 <= index < self.len()*

Computes in **O(1)** time (average).

source### impl<T, S> IndexSet<T, S>where

T: Eq + Hash,

S: BuildHasher,

### impl<T, S> IndexSet<T, S>where

T: Eq + Hash,

S: BuildHasher,

source#### pub fn is_disjoint<S2>(&self, other: &IndexSet<T, S2>) -> boolwhere

S2: BuildHasher,

#### pub fn is_disjoint<S2>(&self, other: &IndexSet<T, S2>) -> boolwhere

S2: BuildHasher,

Returns `true`

if `self`

has no elements in common with `other`

.

source#### pub fn is_subset<S2>(&self, other: &IndexSet<T, S2>) -> boolwhere

S2: BuildHasher,

#### pub fn is_subset<S2>(&self, other: &IndexSet<T, S2>) -> boolwhere

S2: BuildHasher,

Returns `true`

if all elements of `self`

are contained in `other`

.

source#### pub fn is_superset<S2>(&self, other: &IndexSet<T, S2>) -> boolwhere

S2: BuildHasher,

#### pub fn is_superset<S2>(&self, other: &IndexSet<T, S2>) -> boolwhere

S2: BuildHasher,

Returns `true`

if all elements of `other`

are contained in `self`

.

## Trait Implementations

source### impl<'a, 'b, T, S1, S2> BitAnd<&'b IndexSet<T, S2>> for &'a IndexSet<T, S1>where

T: Eq + Hash + Clone,

S1: BuildHasher + Default,

S2: BuildHasher,

### impl<'a, 'b, T, S1, S2> BitAnd<&'b IndexSet<T, S2>> for &'a IndexSet<T, S1>where

T: Eq + Hash + Clone,

S1: BuildHasher + Default,

S2: BuildHasher,

source### impl<'a, 'b, T, S1, S2> BitOr<&'b IndexSet<T, S2>> for &'a IndexSet<T, S1>where

T: Eq + Hash + Clone,

S1: BuildHasher + Default,

S2: BuildHasher,

### impl<'a, 'b, T, S1, S2> BitOr<&'b IndexSet<T, S2>> for &'a IndexSet<T, S1>where

T: Eq + Hash + Clone,

S1: BuildHasher + Default,

S2: BuildHasher,

source### impl<'a, 'b, T, S1, S2> BitXor<&'b IndexSet<T, S2>> for &'a IndexSet<T, S1>where

T: Eq + Hash + Clone,

S1: BuildHasher + Default,

S2: BuildHasher,

### impl<'a, 'b, T, S1, S2> BitXor<&'b IndexSet<T, S2>> for &'a IndexSet<T, S1>where

T: Eq + Hash + Clone,

S1: BuildHasher + Default,

S2: BuildHasher,

source### impl<T, S> Default for IndexSet<T, S>where

S: BuildHasher + Default,

### impl<T, S> Default for IndexSet<T, S>where

S: BuildHasher + Default,

source### impl<'de, T, S> Deserialize<'de> for IndexSet<T, S>where

T: Deserialize<'de> + Eq + Hash,

S: Default + BuildHasher,

### impl<'de, T, S> Deserialize<'de> for IndexSet<T, S>where

T: Deserialize<'de> + Eq + Hash,

S: Default + BuildHasher,

Requires crate feature `"serde-1"`

source#### fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>where

D: Deserializer<'de>,

#### fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>where

D: Deserializer<'de>,

source### impl<'a, T, S> Extend<&'a T> for IndexSet<T, S>where

T: Hash + Eq + Copy,

S: BuildHasher,

### impl<'a, T, S> Extend<&'a T> for IndexSet<T, S>where

T: Hash + Eq + Copy,

S: BuildHasher,

source#### fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iterable: I)

#### fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iterable: I)

source#### fn extend_one(&mut self, item: A)

#### fn extend_one(&mut self, item: A)

`extend_one`

)source#### fn extend_reserve(&mut self, additional: usize)

#### fn extend_reserve(&mut self, additional: usize)

`extend_one`

)source### impl<T, S> Extend<T> for IndexSet<T, S>where

T: Hash + Eq,

S: BuildHasher,

### impl<T, S> Extend<T> for IndexSet<T, S>where

T: Hash + Eq,

S: BuildHasher,

source#### fn extend<I: IntoIterator<Item = T>>(&mut self, iterable: I)

#### fn extend<I: IntoIterator<Item = T>>(&mut self, iterable: I)

source#### fn extend_one(&mut self, item: A)

#### fn extend_one(&mut self, item: A)

`extend_one`

)source#### fn extend_reserve(&mut self, additional: usize)

#### fn extend_reserve(&mut self, additional: usize)

`extend_one`

)source### impl<T, S> FromIterator<T> for IndexSet<T, S>where

T: Hash + Eq,

S: BuildHasher + Default,

### impl<T, S> FromIterator<T> for IndexSet<T, S>where

T: Hash + Eq,

S: BuildHasher + Default,

source#### fn from_iter<I: IntoIterator<Item = T>>(iterable: I) -> Self

#### fn from_iter<I: IntoIterator<Item = T>>(iterable: I) -> Self

source### impl<'a, T, S> IntoIterator for &'a IndexSet<T, S>where

T: Hash + Eq,

S: BuildHasher,

### impl<'a, T, S> IntoIterator for &'a IndexSet<T, S>where

T: Hash + Eq,

S: BuildHasher,

source### impl<T, S> IntoIterator for IndexSet<T, S>where

T: Hash + Eq,

S: BuildHasher,

### impl<T, S> IntoIterator for IndexSet<T, S>where

T: Hash + Eq,

S: BuildHasher,

source### impl<T, S1, S2> PartialEq<IndexSet<T, S2>> for IndexSet<T, S1>where

T: Hash + Eq,

S1: BuildHasher,

S2: BuildHasher,

### impl<T, S1, S2> PartialEq<IndexSet<T, S2>> for IndexSet<T, S1>where

T: Hash + Eq,

S1: BuildHasher,

S2: BuildHasher,

source### impl<T, S> Serialize for IndexSet<T, S>where

T: Serialize + Hash + Eq,

S: BuildHasher,

### impl<T, S> Serialize for IndexSet<T, S>where

T: Serialize + Hash + Eq,

S: BuildHasher,

Requires crate feature `"serde-1"`