sfl::small_flat_set

Table of Contents

Summary
Template Parameters
Public Member Types
Public Data Members
Public Member Functions
- (constructor)
- (destructor)
- operator=
- get_allocator
- key_comp
- value_comp
- begin, cbegin
- end, cend
- rbegin, crbegin
- rend, crend
- nth
- index_of
- empty
- size
- max_size
- capacity
- available
- reserve
- shrink_to_fit
- clear
- emplace
- emplace_hint
- insert
- erase
- swap
- lower_bound
- upper_bound
- equal_range
- find
- count
- contains
- data
Non-member Functions
- operator==
- operator!=
- operator<
- operator>
- operator<=
- operator>=
- swap
- erase_if

Summary

Defined in header sfl/small_flat_set.hpp:

namespace sfl
{
    template < typename Key,
               std::size_t N,
               typename Compare = std::less<Key>,
               typename Allocator = std::allocator<Key> >
    class small_flat_set;
}

sfl::small_flat_set is an associative container similar to std::set, but the underlying storage is implemented as a sorted vector.

sfl::small_flat_set 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.

The complexity of insertion or removal of elements is O(N). The complexity of search is O(log N).

The elements of sfl::small_flat_set are always stored contiguously in the memory.

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

sfl::small_flat_set meets the requirements of Container, AllocatorAwareContainer, ReversibleContainer, ContiguousContainer and AssociativeContainer.

Template Parameters

```
typename Key
```
Key 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 Compare
```
Ordering function for 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 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_compare`	`Compare`
`value_compare`	`Compare`
`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`
`reverse_iterator`	`std::reverse_iterator<iterator>`
`const_reverse_iterator`	`std::reverse_iterator<const_iterator>`

Public Data Members

static constexpr size_type static_capacity = N;

Public Member Functions

(constructor)

small_flat_set() noexcept(
    std::is_nothrow_default_constructible<Allocator>::value &&
    std::is_nothrow_default_constructible<Compare>::value
);

explicit small_flat_set(const Compare& comp) noexcept(
    std::is_nothrow_default_constructible<Allocator>::value &&
    std::is_nothrow_copy_constructible<Compare>::value
);

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

explicit small_flat_set(const Compare& comp, const Allocator& alloc) noexcept(
    std::is_nothrow_copy_constructible<Allocator>::value &&
    std::is_nothrow_copy_constructible<Compare>::value
);

Effects: Constructs an empty container.

Complexity: Constant.

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

template <typename InputIt>
small_flat_set(InputIt first, InputIt last, const Compare& comp);

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

```
template <typename InputIt>
small_flat_set(InputIt first, InputIt last, const Compare& comp, const Allocator& alloc);
```
Effects: Constructs an empty container and inserts elements from the range [first, last).

Note: These overloads participate in overload resolution only if InputIt satisfies requirements of LegacyInputIterator.

Complexity: Linear in std::distance(first, last).

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

small_flat_set(std::initializer_list<value_type> ilist, const Compare& comp);

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

```
small_flat_set(std::initializer_list<value_type> ilist, const Compare& comp, const Allocator& alloc);
```
Effects: Constructs an empty container and inserts elements from the initializer list ilist.

Complexity: Linear in ilist.size().

small_flat_set(const small_flat_set& other);

```
small_flat_set(const small_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().

small_flat_set(small_flat_set&& other);

```
small_flat_set(small_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.

(destructor)

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

Complexity: Linear in size().

operator=

```
small_flat_set& operator=(const small_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().
```
small_flat_set& operator=(small_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().
```
small_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

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

Complexity: Constant.

key_comp

```
key_compare key_comp() const;
```
Effects: Returns the function object that compares the keys, which is a copy of this container's constructor argument comp.

Complexity: Constant.

value_comp

```
value_compare value_comp() 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.

rbegin, crbegin

```
reverse_iterator rbegin() noexcept;
```

const_reverse_iterator rbegin() const noexcept;

```
const_reverse_iterator crbegin() const noexcept;
```
Effects: Returns a reverse iterator to the first element of the reversed container. It corresponds to the last element of the non-reversed container. If the container is empty, the returned iterator is equal to rend().

Complexity: Constant.

rend, crend

```
reverse_iterator rend() noexcept;
```

const_reverse_iterator rend() const noexcept;

```
const_reverse_iterator crend() const noexcept;
```
Effects: Returns a reverse iterator to the element following the last element of the reversed container. It corresponds to the element preceding the first element of the non-reversed 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>
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

```
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.

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

insert

```
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.
```
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.
```
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 Compare::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.
```
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.

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

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

Note: This overload participates in overload resolution only if all following conditions are satisfied:
1. Compare::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.
```
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()).

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 the element (if one exists) with the key equivalent to key or x.

Note: Overload (5) participates in overload resolution only if Compare::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

```
void swap(small_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.

lower_bound

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

const_iterator lower_bound(const Key& key) const;

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

```
template <typename K>
const_iterator lower_bound(const K& x) const;
```
Effects: Returns an iterator pointing to the first element with key that compares not less than key or x. Returns end() if no such element is found.

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

Complexity: Logarithmic in size().

upper_bound

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

const_iterator upper_bound(const Key& key) const;

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

```
template <typename K>
const_iterator upper_bound(const K& x) const;
```
Effects: Returns an iterator pointing to the first element with key that compares greater than key or x. Returns end() if no such element is found.

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

Complexity: Logarithmic in size().

equal_range

std::pair<iterator, iterator> equal_range(const Key& key);

std::pair<const_iterator, const_iterator> equal_range(const Key& key) const;

template <typename K>
std::pair<iterator, iterator> equal_range(const K& x);

```
template <typename K>
std::pair<const_iterator, const_iterator> equal_range(const K& x) const;
```
Effects: Returns a range containing all elements with key that compares equivalent to key or x.
- The first iterator in pair points to the first element that compares not less than key or x. It is equal to end() if no such element is found.
- The second iterator in pair points to the first element that compares greater than key or x. It is equal to end() is no such element is found.
Note: Overloads (3) and (4) participate in overload resolution only if Compare::is_transparent exists and is a valid type. It allows calling these functions without constructing an instance of Key.

Complexity: Logarithmic in size().

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.

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

Complexity: Logarithmic in size().

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, which is either 1 or 0 since this container does not allow duplicates.

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

Complexity: Logarithmic 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 Compare::is_transparent exists and is a valid type. It allows calling this function without constructing an instance of Key.

Complexity: Logarithmic in size().

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, std::size_t N, typename C, typename A>
bool operator==
(
    const small_flat_set<K, N, C, A>& x,
    const small_flat_set<K, N, C, 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()
- Each element in x compares equal with the element in y at the same position.
The comparison is performed by std::equal. This comparison ignores the container's ordering Compare.

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

operator!=

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

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

For details see operator==.

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

operator<

```
template <typename K, std::size_t N, typename C, typename A>
bool operator<
(
    const small_flat_set<K, N, C, A>& x,
    const small_flat_set<K, N, C, A>& y
);
```
Effects: Compares the contents of x and y lexicographically. The comparison is performed by a function std::lexicographical_compare. This comparison ignores the container's ordering Compare.

Returns: true if the contents of the x are lexicographically less than the contents of y, false otherwise.

operator>

```
template <typename K, std::size_t N, typename C, typename A>
bool operator>
(
    const small_flat_set<K, N, C, A>& x,
    const small_flat_set<K, N, C, A>& y
);
```
Effects: Compares the contents of lhs and rhs lexicographically.

The comparison is performed by a function std::lexicographical_compare. This comparison ignores the container's ordering Compare.

Returns: true if the contents of the x are lexicographically greater than the contents of y, false otherwise.

operator<=

```
template <typename K, std::size_t N, typename C, typename A>
bool operator<=
(
    const small_flat_set<K, N, C, A>& x,
    const small_flat_set<K, N, C, A>& y
);
```
Effects: Compares the contents of x and y lexicographically. The comparison is performed by a function std::lexicographical_compare. This comparison ignores the container's ordering Compare.

Returns: true if the contents of the x are lexicographically less than or equal to the contents of y, false otherwise.

operator>=

```
template <typename K, std::size_t N, typename C, typename A>
bool operator>=
(
    const small_flat_set<K, N, C, A>& x,
    const small_flat_set<K, N, C, A>& y
);
```
Effects: Compares the contents of x and y lexicographically. The comparison is performed by a function std::lexicographical_compare. This comparison ignores the container's ordering Compare.

Returns: true if the contents of the x are lexicographically greater than or equal to the contents of y, false otherwise.

swap

template <typename K, std::size_t N, typename C, typename A>
void swap
(
    small_flat_set<K, N, C, A>& x,
    small_flat_set<K, N, C, A>& y
);

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

erase_if

```
template <typename K, std::size_t N, typename C, typename A, typename Predicate>
typename small_flat_set<K, N, C, A>::size_type
    erase_if(small_flat_set<K, N, C, 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.

Files

small_flat_set.md

Latest commit

History

small_flat_set.md

File metadata and controls

sfl::small_flat_set

Summary

Template Parameters

Public Member Types

Public Data Members

Public Member Functions

(constructor)

(destructor)

operator=

get_allocator

key_comp

value_comp

begin, cbegin

end, cend

rbegin, crbegin

rend, crend

nth

index_of

empty

size

max_size

capacity

available

reserve

shrink_to_fit

clear

emplace

emplace_hint

insert

erase

swap

lower_bound

upper_bound

equal_range

find

count

contains

data

Non-member Functions

operator==

operator!=

operator<

operator>

operator<=

operator>=

swap

erase_if