[#bsl-unordered_set-0d2d]
= xref:bsl.adoc[bsl]::unordered_set
:relfileprefix: ../
:mrdocs:

This class template implements a value‐semantic container type holding an unordered set of unique values (of template parameter type `KEY`).

== Synopsis

Declared in `<bslstl_unorderedset.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    class KEY,
    class HASH = xref:bsl/hash-06.adoc[bsl::hash<KEY>],
    class EQUAL = xref:bsl/equal_to-0d.adoc[bsl::equal_to<KEY>],
    class ALLOCATOR = xref:bsl/allocator-0df.adoc[bsl::allocator<KEY>]>
class unordered_set;
----

== Description

This class: * supports a complete set of _value‐semantic_ operations

* except for BDEX serialization * is _exception‐neutral_ (agnostic except for the `at` method) * is _alias‐safe_ * is `const` _thread‐safe_ For terminology see {`bsldoc_glossary`}.

== Type Aliases

[cols="1,4"]
|===
| Name| Description
| xref:bsl/unordered_set-0d2d/allocator_type.adoc[`allocator_type`] 
| This `typedef` is an alias to the (template parameter) `ALLOCATOR`.
| xref:bsl/unordered_set-0d2d/const_iterator.adoc[`const_iterator`] 
| This `typedef` is an alias to `iterator`.
| xref:bsl/unordered_set-0d2d/const_local_iterator.adoc[`const_local_iterator`] 
| This `typedef` is an alias to `local_iterator`.
| xref:bsl/unordered_set-0d2d/const_pointer.adoc[`const_pointer`] 
| This `typedef` is an alias to the allocator const‐pointer type.
| xref:bsl/unordered_set-0d2d/const_reference.adoc[`const_reference`] 
| This `typedef` is an alias to `const value_type&`.
| xref:bsl/unordered_set-0d2d/difference_type.adoc[`difference_type`] 
| This `typedef` is an alias to the allocator difference type.
| xref:bsl/unordered_set-0d2d/hasher.adoc[`hasher`] 
| This `typedef` is an alias to the (template parameter) `HASH` type.
| xref:bsl/unordered_set-0d2d/iterator.adoc[`iterator`] 
| This `typedef` is an alias to the hash‐table iterator type.
| xref:bsl/unordered_set-0d2d/key_equal.adoc[`key_equal`] 
| This `typedef` is an alias to the (template parameter) `EQUAL` type.
| xref:bsl/unordered_set-0d2d/key_type.adoc[`key_type`] 
| This `typedef` is an alias to the (template parameter) `KEY` type.
| xref:bsl/unordered_set-0d2d/local_iterator.adoc[`local_iterator`] 
| This `typedef` is an alias for `local_iterator`.
| xref:bsl/unordered_set-0d2d/pointer.adoc[`pointer`] 
| This `typedef` is an alias to the allocator pointer type.
| xref:bsl/unordered_set-0d2d/reference.adoc[`reference`] 
| This `typedef` is an alias to `value_type&`.
| xref:bsl/unordered_set-0d2d/size_type.adoc[`size_type`] 
| This `typedef` is an alias to the allocator size type.
| xref:bsl/unordered_set-0d2d/value_type.adoc[`value_type`] 
| This `typedef` is an alias to `key_type`.
|===


== Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:bsl/unordered_set-0d2d/2constructor-059.adoc[`unordered_set`]         [.small]#[constructor]#
| Constructors
| xref:bsl/unordered_set-0d2d/2destructor.adoc[`~unordered_set`] [.small]#[destructor]#
| Destroy this object.
| xref:bsl/unordered_set-0d2d/operator_assign-0e.adoc[`operator=`] 
| Assignment operators
| xref:bsl/unordered_set-0d2d/begin-0f.adoc[`begin`] 
| `begin` overloads
| xref:bsl/unordered_set-0d2d/bucket-0d.adoc[`bucket`] 
| Return the bucket index for the specified `key`.
| xref:bsl/unordered_set-0d2d/bucket_count.adoc[`bucket_count`] 
| Return the number of buckets in the array of buckets maintained by this set.
| xref:bsl/unordered_set-0d2d/bucket_size.adoc[`bucket_size`] 
| Return the number of elements in the bucket at `index`.
| xref:bsl/unordered_set-0d2d/cbegin-07.adoc[`cbegin`] 
| `cbegin` overloads
| xref:bsl/unordered_set-0d2d/cend-0c.adoc[`cend`] 
| `cend` overloads
| xref:bsl/unordered_set-0d2d/clear.adoc[`clear`] 
| Remove all entries from this unordered set. Note that the set is empty after this call, but allocated memory may be retained for future use.
| xref:bsl/unordered_set-0d2d/contains-05.adoc[`contains`] 
| `contains` overloads
| xref:bsl/unordered_set-0d2d/count-0ca.adoc[`count`] 
| Return the number of elements equivalent to `key`.
| xref:bsl/unordered_set-0d2d/emplace.adoc[`emplace`] 
| Emplace a newly constructed element if the key is missing.
| xref:bsl/unordered_set-0d2d/emplace_hint.adoc[`emplace_hint`] 
| Emplace a newly constructed element using `hint` if the key is missing.
| xref:bsl/unordered_set-0d2d/empty.adoc[`empty`] 
| Return `true` if this set contains no elements, and `false` otherwise.
| xref:bsl/unordered_set-0d2d/end-0b.adoc[`end`] 
| `end` overloads
| xref:bsl/unordered_set-0d2d/equal_range-04f.adoc[`equal_range`] 
| Return the range of elements equivalent to `key`.
| xref:bsl/unordered_set-0d2d/erase-02.adoc[`erase`] 
| `erase` overloads
| xref:bsl/unordered_set-0d2d/find-00e.adoc[`find`] 
| Return an iterator to the element equivalent to `key`.
| xref:bsl/unordered_set-0d2d/get_allocator.adoc[`get_allocator`] 
| Return (a copy of) the allocator used for memory allocation by this unordered set.
| xref:bsl/unordered_set-0d2d/hash_function.adoc[`hash_function`] 
| Return (a copy of) the hash unary functor used by this set to generate a hash value (of type `size_t`) for a `key_type` object.
| xref:bsl/unordered_set-0d2d/insert-0c.adoc[`insert`] 
| `insert` overloads
| xref:bsl/unordered_set-0d2d/insert_range.adoc[`insert_range`] 
| Insert values from `range` if their keys are missing.
| xref:bsl/unordered_set-0d2d/key_eq.adoc[`key_eq`] 
| Return (a copy of) the key‐equality binary functor that returns `true` if the value of two `key_type` objects are equivalent, and `false` otherwise.
| xref:bsl/unordered_set-0d2d/load_factor.adoc[`load_factor`] 
| Return the current load factor of this container.
| xref:bsl/unordered_set-0d2d/max_bucket_count.adoc[`max_bucket_count`] 
| Return a theoretical upper bound on the number of buckets.
| xref:bsl/unordered_set-0d2d/max_load_factor-05.adoc[`max_load_factor`] 
| `max_load_factor` overloads
| xref:bsl/unordered_set-0d2d/max_size.adoc[`max_size`] 
| Return a theoretical upper bound on this set's size.
| xref:bsl/unordered_set-0d2d/rehash.adoc[`rehash`] 
| Rehash this set to have at least `numBuckets` buckets.
| xref:bsl/unordered_set-0d2d/reserve.adoc[`reserve`] 
| Reserve capacity for at least `numElements` elements.
| xref:bsl/unordered_set-0d2d/size.adoc[`size`] 
| Return the number of elements in this set.
| xref:bsl/unordered_set-0d2d/swap.adoc[`swap`] 
| Exchange the contents of this set with `other`.
| xref:bsl/unordered_set-0d2d/2conversion.adoc[`operator BloombergLP::bslmf::NestedTraitDeclaration<unordered_set, IsBitwiseMoveable, ::BloombergLP::bslmf::IsBitwiseMoveable<HashTable>::value>`] 
| Return the nested trait declaration for `bslmf::IsBitwiseMoveable`.
|===


== Deduction Guides

[cols="1,4"]
|===
| Name| Description
| xref:bsl/unordered_set-0c5.adoc[`unordered_set<KEY>`] 
| CTAD guide: deduce `KEY` from initializer_list `value_type`.
| xref:bsl/unordered_set-0b5.adoc[`unordered_set<KEY>`] 
| CTAD guide: deduce `KEY` from initializer_list `value_type`.
| xref:bsl/unordered_set-0f.adoc[`unordered_set<KEY>`] 
| CTAD guide: deduce `KEY` from iterator `value_type`.
| xref:bsl/unordered_set-05.adoc[`unordered_set<KEY>`] 
| CTAD guide: deduce `KEY` from iterator `value_type`.
| xref:bsl/unordered_set-0d25.adoc[`unordered_set<KEY, HASH>`] 
| CTAD guide: deduce `KEY` from initializer_list `value_type`.
| xref:bsl/unordered_set-0c2.adoc[`unordered_set<KEY, HASH>`] 
| CTAD guide: deduce `KEY` from iterator `value_type`.
| xref:bsl/unordered_set-088.adoc[`unordered_set<KEY, HASH, EQUAL>`] 
| CTAD guide: deduce `KEY` from initializer_list `value_type`.
| xref:bsl/unordered_set-02f.adoc[`unordered_set<KEY, HASH, EQUAL>`] 
| CTAD guide: deduce `KEY` from iterator `value_type`.
| xref:bsl/unordered_set-0b4.adoc[`unordered_set<KEY, HASH, EQUAL, ALLOCATOR>`] 
| CTAD guide: deduce `KEY` from initializer_list `value_type`.
| xref:bsl/unordered_set-0e.adoc[`unordered_set<KEY, HASH, EQUAL, ALLOCATOR>`] 
| CTAD guide: deduce `KEY` from iterator `value_type`.
| xref:bsl/unordered_set-07.adoc[`unordered_set<KEY, HASH, bsl::equal_to<KEY>, ALLOCATOR>`] 
| CTAD guide: deduce `KEY` from initializer_list `value_type`.
| xref:bsl/unordered_set-087.adoc[`unordered_set<KEY, HASH, bsl::equal_to<KEY>, ALLOCATOR>`] 
| CTAD guide: deduce `KEY` from iterator `value_type`.
| xref:bsl/unordered_set-048.adoc[`unordered_set<KEY, bsl::hash<KEY>, bsl::equal_to<KEY>, ALLOCATOR>`] 
| CTAD guide: deduce `KEY` from initializer_list `value_type`.
| xref:bsl/unordered_set-0d0.adoc[`unordered_set<KEY, bsl::hash<KEY>, bsl::equal_to<KEY>, ALLOCATOR>`] 
| CTAD guide: deduce `KEY` from initializer_list `value_type`.
| xref:bsl/unordered_set-0ce.adoc[`unordered_set<KEY, bsl::hash<KEY>, bsl::equal_to<KEY>, ALLOCATOR>`] 
| CTAD guide: deduce `KEY` from iterator `value_type`.
| xref:bsl/unordered_set-04b.adoc[`unordered_set<KEY, bsl::hash<KEY>, bsl::equal_to<KEY>, ALLOCATOR>`] 
| CTAD guide: deduce `KEY` from iterator `value_type`.
|===


== Friends

[cols="1,4"]
|===
| Name| Description
| `xref:bsl/operator_eq-087.adoc[bsl::operator==]`
| Return `true` if the specified `lhs` and `rhs` objects have the same value, and `false` otherwise.
|===

== Non-Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:bsl/erase_if-0d.adoc[`erase_if`]
| Erase elements from `s` that satisfy `predicate`.
| xref:bsl/operator_eq-0b3.adoc[`operator==`]
| Return `true` if `lhs` and `rhs` have the same value, and `false` otherwise.
| xref:bsl/swap-05b.adoc[`swap`]
| Exchange the contents of `a` and `b`.
|===


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