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```c++ unordered_map& operator=(unordered_map&& other) noexcept(boost::allocator_traits<Allocator>::is_always_equal::value && boost::is_nothrow_move_assignable_v<Hash> && boost::is_nothrow_move_assignable_v<Pred>); ``` The move assignment operator.
If `Alloc::propagate_on_container_move_assignment` exists and `Alloc::propagate_on_container_move_assignment::value` is `true`, the allocator is overwritten, if not the moved elements are created using the existing allocator.
Requires:;; `value_type` is move constructible.
Initializer List Assignment
```c++ unordered_map& operator=(std::initializer_list<value_type> il); ```
Assign from values in initializer list. All existing elements are either overwritten by the new elements or destroyed.
Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/CopyInsertable[CopyInsertable^] into the container and https://en.cppreference.com/w/cpp/named_req/CopyAssignable[CopyAssignable^].
Iterators
```c++ iterator begin() noexcept; const_iterator begin() const noexcept; ```
Returns:;; An iterator referring to the first element of the container, or if the container is empty the past-the-end value for the container.
```c++ iterator end() noexcept; const_iterator end() const noexcept; ```
Returns:;; An iterator which refers to the past-the-end value for the container.
```c++ const_iterator cbegin() const noexcept; ```
Returns:;; A `const_iterator` referring to the first element of the container, or if the container is empty the past-the-end value for the container.
```c++ const_iterator cend() const noexcept; ```
Returns:;; A `const_iterator` which refers to the past-the-end value for the container.
Size and Capacity
empty
```c++ [[nodiscard]] bool empty() const noexcept; ```
Returns:;; `size() == 0`
size
```c++ size_type size() const noexcept; ```
Returns:;; `std::distance(begin(), end())`
max_size
```c++ size_type max_size() const noexcept; ```
Returns:;; `size()` of the largest possible container.
Modifiers
emplace
```c++ template<class... Args> std::pair<iterator, bool> emplace(Args&&... args); ```
Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/EmplaceConstructible[EmplaceConstructible^] into `X` from `args`. Returns:;; The bool component of the return type is true if an insert took place. + + If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the element with equivalent key. Throws:;; If an exception is thrown by an operation other than a call to `hasher` the function has no effect. Notes:;; Can invalidate iterators, but only if the insert causes the load factor to be greater to or equal to the maximum load factor. + + Pointers and references to elements are never invalidated. + + If `args...` is of the form `k,v`, it delays constructing the whole object until it is certain that an element should be inserted, using only the `k` argument to check. This optimization happens when the map's `key_type` is move constructible or when the `k` argument is a `key_type`.

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Returns:;; A `const_iterator` which refers to the past-the-end value for the container.
Returns:;; A `const_iterator` which refers to the past-the-end value for the container.
06/05/2026
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read-only, safe-html, strict-same
Unit identifier
44338
Source string location
:728
String age
06/05/2026
Last updated
06/05/2026
Source string age
06/05/2026
Translation file AsciiDoc file
doc/modules/ROOT/pages/reference/unordered_map.adoc, string 159