small_unordered_flat_set.md

sfl::small_unordered_flat_set

Table of Contents

• Summary
• Template Parameters
• Public Member Types
• Public Data Members
  • static_capacity
• Public Member Functions
  • (constructor)
  • (destructor)
  • operator=
  • get_allocator
  • key_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_set.hpp:

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

sfl::small_unordered_flat_set is an associative container that contains unsorted set of unique objects of type Key.

Underlying storage is implemented as unsorted vector.

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

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

Template Parameters

1. typename Key
   

   Key type.

2. 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.

3. typename KeyEqual
   

   Function for comparing keys.

4. 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 Key.

Public Member Types

Member Type	Definition
allocator_type	Allocator
allocator_traits	std::allocator_traits<allocator_type>
key_type	Key
value_type	Key
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 const value_type
const_iterator	LegacyRandomAccessIterator and LegacyContiguousIterator to const value_type

Public Data Members

static_capacity

static constexpr size_type static_capacity = N;

Public Member Functions

(constructor)

1. small_unordered_flat_set() noexcept(
       std::is_nothrow_default_constructible<Allocator>::value &&
       std::is_nothrow_default_constructible<KeyEqual>::value
   );
   

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

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

4. explicit small_unordered_flat_set(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.

   
   
   

5. template <typename InputIt>
   small_unordered_flat_set(InputIt first, InputIt last);
   

6. template <typename InputIt>
   small_unordered_flat_set(InputIt first, InputIt last, const KeyEqual& equal);
   

7. template <typename InputIt>
   small_unordered_flat_set(InputIt first, InputIt last, const Allocator& alloc);
   

8. template <typename InputIt>
   small_unordered_flat_set(InputIt first, InputIt last, const KeyEqual& equal, const Allocator& alloc);
   

   Effects: Constructs the container with the contents of the range [first, last).

   If multiple elements in the range have keys that compare equivalent, then the first element is inserted.

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

   
   
   

9. small_unordered_flat_set(std::initializer_list<value_type> ilist);
   

10. small_unordered_flat_set(std::initializer_list<value_type> ilist, const KeyEqual& equal);
    

11. small_unordered_flat_set(std::initializer_list<value_type> ilist, const Allocator& alloc);
    

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

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

    If multiple elements in the range have keys that compare equivalent, then the first element is inserted.

    
    
    

13. small_unordered_flat_set(const small_unordered_flat_set& other);
    

14. small_unordered_flat_set(const small_unordered_flat_set& other, const Allocator& alloc);
    

    Effects: Copy constructor. Constructs the container with the copy of the contents of other.

    Complexity: Linear in other.size().

    
    
    

15. small_unordered_flat_set(small_unordered_flat_set&& other);
    

16. small_unordered_flat_set(small_unordered_flat_set&& 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.

    
    
    

17. template <typename Range>
    small_unordered_flat_set(sfl::from_range_t, Range&& range);
    

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

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

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

    Effects: Constructs the container with the contents of range.

    If multiple elements in the range have keys that compare equivalent, then the first element is inserted.

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

    
    
    

(destructor)

1. ~small_unordered_flat_set();
   

   Effects: Destructs the container. The destructors of the elements are called and the used storage is deallocated.

   Complexity: Linear in size().

   
   
   

operator=

1. small_unordered_flat_set& operator=(const small_unordered_flat_set& 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().

   
   
   

2. small_unordered_flat_set& operator=(small_unordered_flat_set&& 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().

   
   
   

3. small_unordered_flat_set& operator=(std::initializer_list<Key> 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

1. allocator_type get_allocator() const noexcept;
   

   Effects: Returns the allocator associated with the container.

   Complexity: Constant.

   
   
   

key_eq

1. 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.

   
   
   

begin, cbegin

1. iterator begin() noexcept;
   

2. const_iterator begin() const noexcept;
   

3. 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

1. iterator end() noexcept;
   

2. const_iterator end() const noexcept;
   

3. 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

1. iterator nth(size_type pos) noexcept;
   

2. 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

1. 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

1. bool empty() const noexcept;
   

   Effects: Returns true if the container has no elements, i.e. whether begin() == end().

   Complexity: Constant.

   
   
   

size

1. size_type size() const noexcept;
   

   Effects: Returns the number of elements in the container, i.e. std::distance(begin(), end()).

   Complexity: Constant.

   
   
   

max_size

1. 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

1. size_type capacity() const noexcept;
   

   Effects: Returns the number of elements that the container has currently allocated space for.

   Complexity: Constant.

   
   
   

available

1. 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

1. 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

1. 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

1. 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

1. template <typename... Args>
   std::pair<iterator, bool> emplace(Args&&... args);
   

   Effects: Inserts new element into the container if the container doesn't already contain an element with an equivalent key.

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

   The element may be constructed even if there already is an element with the key in the container, in which case the newly constructed element will be destroyed immediately.

   Returns: The iterator component points to the inserted element or to the already existing element. The bool component is true if insertion happened and false if it did not.

   
   
   

emplace_hint

1. template <typename... Args>
   iterator emplace_hint(const_iterator hint, Args&&... args);
   

   Preconditions: cbegin() <= hint && hint <= cend()

   Effects: Inserts new element into the container if the container doesn't already contain an element with an equivalent key.

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

   The element may be constructed even if there already is an element with the key in the container, in which case the newly constructed element will be destroyed immediately.

   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 or to the already existing element.

   
   
   

insert

1. std::pair<iterator, bool> insert(const value_type& value);
   

   Effects: Inserts copy of value if the container doesn't already contain an element with an equivalent key.

   Returns: The iterator component points to the inserted element or to the already existing element. The bool component is true if insertion happened and false if it did not.

   
   
   

2. std::pair<iterator, bool> insert(value_type&& value);
   

   Effects: Inserts value using move semantics if the container doesn't already contain an element with an equivalent key.

   Returns: The iterator component points to the inserted element or to the already existing element. The bool component is true if insertion happened and false if it did not.

   
   
   

3. template <typename K>
   std::pair<iterator, bool> insert(K&& x);
   

   Effects: Inserts new element if the container doesn't already contain an element with a key equivalent to x.

   New element is constructed as value_type(std::forward<K>(x)).

   Note: This overload 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: The iterator component points to the inserted element or to the already existing element. The bool component is true if insertion happened and false if it did not.

   
   
   

4. iterator insert(const_iterator hint, const value_type& value);
   

   Preconditions: cbegin() <= hint && hint <= cend()

   Effects: Inserts copy of value if the container doesn't already contain an element with an equivalent key.

   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 or to the already existing element.

   
   
   

5. iterator insert(const_iterator hint, value_type&& value);
   

   Preconditions: cbegin() <= hint && hint <= cend()

   Effects: Inserts value using move semantics if the container doesn't already contain an element with an equivalent key.

   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 or to the already existing element.

   
   
   

6. template <typename K>
   iterator insert(const_iterator hint, K&& x);
   

   Preconditions: cbegin() <= hint && hint <= cend()

   Effects: Inserts new element if the container doesn't already contain an element with a key equivalent to x.

   New element is constructed as value_type(std::forward<K>(x)).

   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 all following conditions are satisfied:

   1. KeyEqual::is_transparent exists and is a valid type. It allows calling this function without constructing an instance of Key.
   2. std::is_convertible_v<K&&, iterator> is false.
   3. std::is_convertible_v<K&&, const_iterator> is false.

   Returns: Iterator to the inserted element or to the already existing element.

   
   
   

7. template <typename InputIt>
   void insert(InputIt first, InputIt last);
   

   Effects: Inserts elements from range [first, last) if the container doesn't already contain an element with an equivalent key.

   If multiple elements in the range have keys that compare equivalent, then the first element is inserted.

   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.

   
   
   

8. void insert(std::initializer_list<value_type> ilist);
   

   Effects: Inserts elements from initializer list ilist if the container doesn't already contain an element with an equivalent key.

   If multiple elements in the range have keys that compare equivalent, then the first element is inserted.

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

   
   
   

insert_range

1. template <typename Range>
   void insert_range(Range&& range);
   

   Effects: Inserts elements from range if the container doesn't already contain an element with an equivalent key.

   If multiple elements in the range have keys that compare equivalent, then the first element is inserted.

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

   
   
   

erase

1. iterator erase(iterator pos);
   

2. iterator erase(const_iterator pos);
   

   Preconditions: cbegin() <= pos && pos < cend()

   Effects: Removes the element at pos.

   Returns: Iterator following the last removed element.

   
   
   

3. 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.

   
   
   

4. size_type erase(const Key& key);
   

5. template <typename K>
   size_type erase(K&& x);
   

   Effects: Removes the element (if one exists) 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 (0 or 1).

   
   
   

swap

1. void swap(small_unordered_flat_set& 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

1. iterator find(const Key& key);
   

2. const_iterator find(const Key& key) const;
   

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

4. 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.

   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

1. size_type count(const Key& key) const;
   

2. template <typename K>
   size_type count(const K& x) const;
   

   Effects: Returns the number of elements with key equivalent to key or x, which is either 1 or 0 since this container does not allow duplicates.

   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.

   
   
   

contains

1. bool contains(const Key& key) const;
   

2. 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

1. value_type* data() noexcept;
   

2. 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==

1. template <typename K, std::size_t N, typename E, typename A>
   bool operator==
   (
       const small_unordered_flat_set<K, N, E, A>& x,
       const small_unordered_flat_set<K, 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!=

1. template <typename K, std::size_t N, typename E, typename A>
   bool operator!=
   (
       const small_unordered_flat_set<K, N, E, A>& x,
       const small_unordered_flat_set<K, 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

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

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

   
   
   

erase_if

1. template <typename K, std::size_t N, typename E, typename A, typename Predicate>
   typename small_unordered_flat_set<K, N, E, A>::size_type
       erase_if(small_unordered_flat_set<K, 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.