sfl::small_unordered_flat_multimap

Table of Contents

Summary
Template Parameters
Public Member Types
Public Member Classes
- value_compare
Public Data Members
- static_capacity
Public Member Functions
- (constructor)
- (destructor)
- operator=
- get_allocator
- key_eq
- value_eq
- begin, cbegin
- end, cend
- nth
- index_of
- empty
- size
- max_size
- capacity
- available
- reserve
- shrink_to_fit
- clear
- emplace
- emplace_hint
- insert
- insert_range
- erase
- swap
- find
- count
- contains
- data
Non-member Functions
- operator==
- operator!=
- swap
- erase_if

Summary

Defined in header sfl/small_unordered_flat_multimap.hpp:

namespace sfl
{
    template < typename Key,
               typename T,
               std::size_t N,
               typename KeyEqual = std::equal_to<Key>,
               typename Allocator = std::allocator<std::pair<Key, T>> >
    class small_unordered_flat_multimap;
}

sfl::small_unordered_flat_multimap is an associative container that contains unsorted set of key-value pairs, while permitting multiple entries with equivalent keys.

Underlying storage is implemented as unsorted vector.

Complexity of search and remove operations is O(N). Complexity of insert operation is O(1).

This container internally holds statically allocated array of size N and stores elements into this array until the number of elements is not greater than N, which avoids dynamic memory allocation and deallocation. The dynamic memory management is used when the number of elements has to be greater than N.

Elements of this container are always stored contiguously in the memory.

Iterators to elements are random access iterators and they meet the requirements of LegacyRandomAccessIterator.

sfl::small_unordered_flat_multimap meets the requirements of Container, AllocatorAwareContainer and ContiguousContainer. The requirements of UnorderedAssociativeContainer are partionally met (this container doesn't use Hash).

Template Parameters

```
typename Key
```
Key type.
```
typename T
```
Value type.
```
std::size_t N
```
Size of the internal statically allocated array, i.e. the maximal number of elements that can fit into this array.

This parameter can be zero.
```
typename KeyEqual
```
Function for comparing keys.
```
typename Allocator
```
Allocator used for memory allocation/deallocation and construction/destruction of elements.

This type must meet the requirements of Allocator.

The program is ill-formed if Allocator::value_type is not the same as std::pair<Key, T>.

Public Member Types

Member Type	Definition
`allocator_type`	`Allocator`
`allocator_traits`	`std::allocator_traits<allocator_type>`
`key_type`	`Key`
`mapped_type`	`T`
`value_type`	`std::pair<Key, T>`
`size_type`	`typename allocator_traits::size_type`
`difference_type`	`typename allocator_traits::difference_type`
`key_equal`	`KeyEqual`
`reference`	`value_type&`
`const_reference`	`const value_type&`
`pointer`	`typename allocator_traits::pointer`
`const_pointer`	`typename allocator_traits::const_pointer`
`iterator`	LegacyRandomAccessIterator and LegacyContiguousIterator to `value_type`
`const_iterator`	LegacyRandomAccessIterator and LegacyContiguousIterator to `const value_type`

Public Member Classes

value_compare

class value_compare
{
public:
    bool operator()(const value_type& x, const value_type& y) const;
};

Public Data Members

static_capacity

static constexpr size_type static_capacity = N;

Public Member Functions

(constructor)

small_unordered_flat_multimap() noexcept(
    std::is_nothrow_default_constructible<Allocator>::value &&
    std::is_nothrow_default_constructible<KeyEqual>::value
);

explicit small_unordered_flat_multimap(const KeyEqual& equal) noexcept(
    std::is_nothrow_default_constructible<Allocator>::value &&
    std::is_nothrow_copy_constructible<KeyEqual>::value
);

explicit small_unordered_flat_multimap(const Allocator& alloc) noexcept(
    std::is_nothrow_copy_constructible<Allocator>::value &&
    std::is_nothrow_default_constructible<KeyEqual>::value
);

explicit small_unordered_flat_multimap(const KeyEqual& equal, const Allocator& alloc) noexcept(
    std::is_nothrow_copy_constructible<Allocator>::value &&
    std::is_nothrow_copy_constructible<KeyEqual>::value
);

Effects: Constructs an empty container.

template <typename InputIt>
small_unordered_flat_multimap(InputIt first, InputIt last);

template <typename InputIt>
small_unordered_flat_multimap(InputIt first, InputIt last, const KeyEqual& equal);

template <typename InputIt>
small_unordered_flat_multimap(InputIt first, InputIt last, const Allocator& alloc);

```
template <typename InputIt>
small_unordered_flat_multimap(InputIt first, InputIt last, const KeyEqual& equal, const Allocator& alloc);
```
Effects: Constructs the container with the contents of the range [first, last).

Note: This overload participates in overload resolution only if InputIt satisfies requirements of LegacyInputIterator.

small_unordered_flat_multimap(std::initializer_list<value_type> ilist);

small_unordered_flat_multimap(std::initializer_list<value_type> ilist, const KeyEqual& equal);

small_unordered_flat_multimap(std::initializer_list<value_type> ilist, const Allocator& alloc);

small_unordered_flat_multimap(std::initializer_list<value_type> ilist, const KeyEqual& equal, const Allocator& alloc);

Effects: Constructs the container with the contents of the initializer list ilist.

small_unordered_flat_multimap(const small_unordered_flat_multimap& other);

```
small_unordered_flat_multimap(const small_unordered_flat_multimap& other, const Allocator& alloc);
```
Effects: Copy constructor. Constructs the container with the copy of the contents of other.

Complexity: Linear in other.size().

small_unordered_flat_multimap(small_unordered_flat_multimap&& other);

```
small_unordered_flat_multimap(small_unordered_flat_multimap&& other, const Allocator& alloc);
```
Effects: Move constructor. Constructs the container with the contents of other using move semantics.

other is not guaranteed to be empty after the move.

other is in a valid but unspecified state after the move.

Complexity: Constant in the best case. Linear in N in the worst case.

template <typename Range>
small_unordered_flat_multimap(sfl::from_range_t, Range&& range);

template <typename Range>
small_unordered_flat_multimap(sfl::from_range_t, Range&& range, const KeyEqual& equal);

template <typename Range>
small_unordered_flat_multimap(sfl::from_range_t, Range&& range, const Allocator& alloc);

template <typename Range>
small_unordered_flat_multimap(sfl::from_range_t, Range&& range, const KeyEqual& equal, const Allocator& alloc);

Effects: Constructs the container with the contents of range.

Note: It is available in C++11. In C++20 are used proper C++20 range concepts.

(destructor)

```
~small_unordered_flat_multimap();
```
Effects: Destructs the container. The destructors of the elements are called and the used storage is deallocated.

Complexity: Linear in size().

operator=

```
small_unordered_flat_multimap& operator=(const small_unordered_flat_multimap& other);
```
Effects: Copy assignment operator. Replaces the contents with a copy of the contents of other.

Returns: *this().

Complexity: Linear in this->size() plus linear in other.size().
```
small_unordered_flat_multimap& operator=(small_unordered_flat_multimap&& other);
```
Effects: Move assignment operator. Replaces the contents with those of other using move semantics.

other is not guaranteed to be empty after the move.

other is in a valid but unspecified state after the move.

Returns: *this().

Complexity:
- The best case: Linear in this->size() plus constant.
- The worst case: Linear in this->size() plus linear in other.size().
```
small_unordered_flat_multimap& operator=(std::initializer_list<value_type> ilist);
```
Effects: Replaces the contents with those identified by initializer list ilist.

Returns: *this().

Complexity: Linear in this->size() plus linear in ilist.size().

get_allocator

```
allocator_type get_allocator() const noexcept;
```
Effects: Returns the allocator associated with the container.

Complexity: Constant.

key_eq

```
key_equal key_eq() const;
```
Effects: Returns the function object that compares keys for equality, which is a copy of this container's constructor argument equal.

Complexity: Constant.

value_eq

```
value_equal value_eq() const;
```
Effects: Returns a function object that compares objects of type value_type.

Complexity: Constant.

begin, cbegin

```
iterator begin() noexcept;
```
```
const_iterator begin() const noexcept;
```
```
const_iterator cbegin() const noexcept;
```
Effects: Returns an iterator to the first element of the container. If the container is empty, the returned iterator will be equal to end().

Complexity: Constant.

end, cend

```
iterator end() noexcept;
```
```
const_iterator end() const noexcept;
```
```
const_iterator cend() const noexcept;
```
Effects: Returns an iterator to the element following the last element of the container. This element acts as a placeholder; attempting to access it results in undefined behavior.

Complexity: Constant.

nth

```
iterator nth(size_type pos) noexcept;
```
```
const_iterator nth(size_type pos) const noexcept;
```
Preconditions: pos <= size()

Effects: Returns an iterator to the element at position pos.

If pos == size(), the returned iterator is equal to end().

Complexity: Constant.

index_of

```
size_type index_of(const_iterator pos) const noexcept;
```
Preconditions: cbegin() <= pos && pos <= cend()

Effects: Returns position of the element pointed by iterator pos, i.e. std::distance(begin(), pos).

If pos == end(), the returned value is equal to size().

Complexity: Constant.

empty

```
bool empty() const noexcept;
```
Effects: Returns true if the container has no elements, i.e. whether begin() == end().

Complexity: Constant.

size

```
size_type size() const noexcept;
```
Effects: Returns the number of elements in the container, i.e. std::distance(begin(), end()).

Complexity: Constant.

max_size

```
size_type max_size() const noexcept;
```
Effects: Returns the maximum number of elements the container is able to hold, i.e. std::distance(begin(), end()) for the largest container.

Complexity: Constant.

capacity

```
size_type capacity() const noexcept;
```
Effects: Returns the number of elements that the container has currently allocated space for.

Complexity: Constant.

available

```
size_type available() const noexcept;
```
Effects: Returns the number of elements that can be inserted into the container without requiring allocation of additional memory.

Complexity: Constant.

reserve

```
void reserve(size_type new_cap);
```
Effects: Tries to increase capacity by allocating additional memory.

If new_cap > capacity(), the function allocates memory for new storage of capacity equal to the value of new_cap, moves elements from old storage to new storage, and deallocates memory used by old storage. Otherwise, the function does nothing.

This function does not change size of the container.

If the capacity is changed, all iterators and all references to the elements are invalidated. Otherwise, no iterators or references are invalidated.

Complexity: Linear.

Exceptions:
- Allocator::allocate may throw.
- T's move or copy constructor may throw.
If an exception is thrown:
- If type T has available noexcept move constructor:
  - This function has no effects (strong exception guarantee).
- Else if type T has available copy constructor:
  - This function has no effects (strong exception guarantee).
- Else if type T has available throwing move constructor:
  - Container is changed but in valid state (basic exception guarantee).

shrink_to_fit

```
void shrink_to_fit();
```
Effects: Tries to reduce memory usage by freeing unused memory.
1. If size() > N && size() < capacity(), the function allocates memory for new storage of capacity equal to the value of size(), moves elements from old storage to new storage, and deallocates memory used by old storage.
2. If size() <= N && N < capacity(), the function sets new storage to be internal statically allocated array of capacity N, moves elements from old storage to new storage, and deallocates memory used by old storage.
3. Otherwise the function does nothing.
This function does not change size of the container.

If the capacity is changed, all iterators and all references to the elements are invalidated. Otherwise, no iterators or references are invalidated.

Complexity: Linear.

Exceptions:
- Allocator::allocate may throw.
- T's move or copy constructor may throw.
If an exception is thrown:
- If type T has available noexcept move constructor:
  - This function has no effects (strong exception guarantee).
- Else if type T has available copy constructor:
  - This function has no effects (strong exception guarantee).
- Else if type T has available throwing move constructor:
  - Container is changed but in valid state (basic exception guarantee).

clear

```
void clear() noexcept;
```
Effects: Erases all elements from the container. After this call, size() returns zero and capacity() remains unchanged.

Complexity: Linear in size().

emplace

```
template <typename... Args>
iterator emplace(Args&&... args);
```
Effects: Inserts a new element into the container.

New element is constructed as value_type(std::forward<Args>(args)...).

Returns: Iterator to the inserted element.

emplace_hint

```
template <typename... Args>
iterator emplace_hint(const_iterator hint, Args&&... args);
```
Preconditions: cbegin() <= hint && hint <= cend()

Effects: Inserts a new element into the container.

New element is constructed as value_type(std::forward<Args>(args)...).

Iterator hint is used as a suggestion where to start to search insert position.

Iterator hint is ignored due to container's underlying storage implementation. This overload exists just to have this container compatible with standard C++ containers as much as possible.

Returns: Iterator to the inserted element.

insert

```
iterator insert(const value_type& value);
```
Effects: Inserts copy of value.

Returns: Iterator to the inserted element.
```
iterator insert(value_type&& value);
```
Effects: Inserts value using move semantics.

Returns: Iterator to the inserted element.
```
template <typename P>
iterator insert(P&& value);
```
Effects: Inserts a new element into the container.

New element is constructed as value_type(std::forward<P>(value)).

Note: This overload participates in overload resolution only if std::is_constructible<value_type, P&&>::value is true.

Returns: Iterator to the inserted element.
```
iterator insert(const_iterator hint, const value_type& value);
```
Preconditions: cbegin() <= hint && hint <= cend()

Effects: Inserts copy of value.

Iterator hint is used as a suggestion where to start to search insert position.

Iterator hint is ignored due to container's underlying storage implementation. This overload exists just to have this container compatible with standard C++ containers as much as possible.

Returns: Iterator to the inserted element.
```
iterator insert(const_iterator hint, value_type&& value);
```
Preconditions: cbegin() <= hint && hint <= cend()

Effects: Inserts value using move semantics.

Iterator hint is used as a suggestion where to start to search insert position.

Iterator hint is ignored due to container's underlying storage implementation. This overload exists just to have this container compatible with standard C++ containers as much as possible.

Returns: Iterator to the inserted element.
```
template <typename P>
iterator insert(const_iterator hint, P&& value);
```
Preconditions: cbegin() <= hint && hint <= cend()

Effects: Inserts a new element into the container.

New element is constructed as value_type(std::forward<P>(value)).

Iterator hint is used as a suggestion where to start to search insert position.

Iterator hint is ignored due to container's underlying storage implementation. This overload exists just to have this container compatible with standard C++ containers as much as possible.

Note: This overload participates in overload resolution only if std::is_constructible<value_type, P&&>::value is true.

Returns: Iterator to the inserted element.
```
template <typename InputIt>
void insert(InputIt first, InputIt last);
```
Effects: Inserts elements from range [first, last).

The call to this function is equivalent to:
```
while (first != last)
{
    insert(*first);
    ++first;
}
```
Note: This overload participates in overload resolution only if InputIt satisfies requirements of LegacyInputIterator.
```
void insert(std::initializer_list<value_type> ilist);
```
Effects: Inserts elements from initializer list ilist.

The call to this function is equivalent to insert(ilist.begin(), ilist.end()).

insert_range

```
template <typename Range>
void insert_range(Range&& range);
```
Effects: Inserts elements from range.

Note: It is available in C++11. In C++20 are used proper C++20 range concepts.

erase

```
iterator erase(iterator pos);
```
```
iterator erase(const_iterator pos);
```
Preconditions: cbegin() <= pos && pos < cend()

Effects: Removes the element at pos.

Returns: Iterator following the last removed element.
```
iterator erase(const_iterator first, const_iterator last);
```
Preconditions: cbegin() <= first && first <= last && last <= cend()

Effects: Removes the elements in the range [first, last).

Returns: Iterator following the last removed element.
```
size_type erase(const Key& key);
```
```
template <typename K>
size_type erase(K&& x);
```
Effects: Removes all elements with the key equivalent to key or x.

Note: Overload (5) participates in overload resolution only if KeyEqual::is_transparent exists and is a valid type. It allows calling this function without constructing an instance of Key.

Returns: Number of elements removed.

swap

```
void swap(small_unordered_flat_multimap& other);
```
Preconditions: allocator_traits::propagate_on_container_swap::value || get_allocator() == other.get_allocator()

Effects: Exchanges the contents of the container with those of other.

Complexity: Constant in the best case. Linear in this->size() plus linear in other.size() in the worst case.

find

```
iterator find(const Key& key);
```

const_iterator find(const Key& key) const;

template <typename K>
iterator find(const K& x);

```
template <typename K>
const_iterator find(const K& x) const;
```
Effects: Returns an iterator pointing to the element with key equivalent to key or x. Returns end() if no such element is found. If there are several elements with key in the container, any of them may be returned.

Note: Overloads (3) and (4) participate in overload resolution only if KeyEqual::is_transparent exists and is a valid type. It allows calling these functions without constructing an instance of Key.

Complexity: Constant in the best case. Linear in size() in the worst case.

count

```
size_type count(const Key& key) const;
```
```
template <typename K>
size_type count(const K& x) const;
```
Effects: Returns the number of elements with key equivalent to key or x.

Note: Overload (2) participates in overload resolution only if KeyEqual::is_transparent exists and is a valid type. It allows calling this function without constructing an instance of Key.

Complexity: Linear in size().

contains

```
bool contains(const Key& key) const;
```
```
template <typename K>
bool contains(const K& x) const;
```
Effects: Returns true if the container contains an element with key equivalent to key or x, otherwise returns false.

Note: Overload (2) participates in overload resolution only if KeyEqual::is_transparent exists and is a valid type. It allows calling this function without constructing an instance of Key.

Complexity: Constant in the best case. Linear in size() in the worst case.

data

```
value_type* data() noexcept;
```
```
const value_type* data() const noexcept;
```
Effects: Returns pointer to the underlying array serving as element storage. The pointer is such that range [data(), data() + size()) is always a valid range, even if the container is empty. data() is not dereferenceable if the container is empty.

Complexity: Constant.

Non-member Functions

operator==

```
template <typename K, typename T, std::size_t N, typename E, typename A>
bool operator==
(
    const small_unordered_flat_multimap<K, T, N, E, A>& x,
    const small_unordered_flat_multimap<K, T, N, E, A>& y
);
```
Effects: Checks if the contents of x and y are equal.

The contents of x and y are equal if the following conditions hold:
- x.size() == y.size()
- For each element in x there is equal element in y.
The comparison is performed by std::is_permutation. This comparison ignores the container's KeyEqual function.

Returns: true if the contents of the x and y are equal, false otherwise.

operator!=

template <typename K, typename T, std::size_t N, typename E, typename A>
bool operator!=
(
    const small_unordered_flat_multimap<K, T, N, E, A>& x,
    const small_unordered_flat_multimap<K, T, N, E, A>& y
);

Effects: Checks if the contents of x and y are equal.

For details see operator==.

Returns: true if the contents of the x and y are not equal, false otherwise.

swap

template <typename K, typename T, std::size_t N, typename E, typename A>
void swap
(
    small_unordered_flat_multimap<K, T, N, E, A>& x,
    small_unordered_flat_multimap<K, T, N, E, A>& y
);

Effects: Swaps the contents of x and y. Calls x.swap(y).

erase_if

template <typename K, typename T, std::size_t N, typename E, typename A, typename Predicate>
typename small_unordered_flat_multimap<K, T, N, E, A>::size_type
    erase_if(small_unordered_flat_multimap<K, T, N, E, A>& c, Predicate pred);

Effects: Erases all elements that satisfy the predicate pred from the container.

pred is unary predicate which returns true if the element should be removed.

Returns: The number of erased elements.

Complexity: Linear.

End of document.

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