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359 lines
8.5 KiB
Markdown
359 lines
8.5 KiB
Markdown
---
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title: "reference_flat_set"
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---
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A fixed capacity set based on a sorted vector.
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The container stores references to objects, rather than the objects themselves.
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The container is an associative lookup table with O(N) insertion and erase, and O(log N) search.
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This container is best used for tables that are occasionally updated and spend most of their time being searched.
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The interface is most similar to `std::set`.
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Uses `etl::less` as the default key comparison method.
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```cpp
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etl::reference_flat_set<typename T, const size_t SIZE, TCompare = etl::less>
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```
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Inherits from `etl::ireference_flat_set<T, TCompare>`.
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`etl::ireference_flat_set` may be used as a size independent pointer or reference type for any `etl::reference_flat_set` instance.
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## Template deduction guides
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C++17 and above
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template <typename... T>
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etl::reference_flat_set(T...)
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### Example
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etl::reference_flat_setdata{ 0, 1, 2, 3, 4, 5, 6, 7 };
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Defines data as a set of int/int pairs, of length 8, containing the supplied data.
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## Make template
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C++11 and above
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template <typename TKey
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typename... T>
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constexpr auto make_reference_flat_set(T&&... values)
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### Example
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auto data = etl::make_reference_flat_set<int>(0, 1, 2, 3, 4, 5, 6, 7);
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## Member types
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```cpp
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key_type T
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value_type T
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size_type size_t
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difference_type ptrdiff_t
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reference value_type&
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const_reference const value_type&
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pointer value_type*
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const_pointer const value_type*
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iterator Random access iterator
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const_iterator Constant random access iterator
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reverse_iterator ETL_OR_STD:reverse_iterator<iterator>
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const_reverse_iterator ETL_OR_STD::reverse_iterator<const_iterator>
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```
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## Constructor
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```cpp
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etl::flat_set<T, SIZE, TCompare>();
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```
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**Description**
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---
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```cpp
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etl::flat_set(const flat_set& other)
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```
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**Description**
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---
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```cpp
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template <typename TIterator>
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etl::flat_set<T, SIZE, TCompare>(TIterator begin, TIterator end);
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```
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**Description**
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If the set is full then raises an `etl::reference_flat_set_full`.
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If asserts or exceptions are not enabled then undefined behaviour occurs.
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## Iterators
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```cpp
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iterator begin()
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const_iterator begin() const
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const_iterator cbegin() const
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```
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**Description**
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Returns an iterator to the beginning of the set.
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---
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```cpp
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iterator end()
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const_iterator end() const
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const_iterator cend() const
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```
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**Description**
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Returns an iterator to the end of the set.
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---
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```cpp
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iterator rbegin()
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const_iterator rbegin() const
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const_iterator crbegin() const
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```
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**Description**
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Returns a reverse iterator to the beginning of the set.
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---
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```cpp
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iterator rend()
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const_iterator rend() const
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const_iterator crend() const
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```
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**Description**
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Returns a reverse iterator to the end of the set.
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## Capacity
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```cpp
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bool empty() const
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```
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**Description**
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Returns `true` if the size of the set is zero, otherwise `false`.
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---
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```cpp
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bool full() const
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```
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**Description**
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Returns `true` if the size of the lookup is `SIZE`, otherwise `false`.
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---
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```cpp
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size_t size() const
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```
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**Description**
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Returns the size of the lookup.
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---
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```cpp
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size_t max_size() const
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```
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**Description**
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Returns the maximum possible size of the set.
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---
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```cpp
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size_t available() const
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```
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**Description**
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Returns the remaining available capacity in the set.
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## Modifiers
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```cpp
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flat_set& operator = (const flat_set& rhs)
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```
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**Description**
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Copies the data from another flat set.
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---
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```cpp
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ETL_OR_STD::pair<iterator, bool> insert(const value_type& value)
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iterator insert(iterator position, const value_type& value)
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```
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**Description**
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---
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```cpp
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template <typename TIterator>
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void insert(TIterator first, TIterator last)
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```
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**Description**
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Inserts values in to the set.
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If the set is full then raises an `etl::reference_flat_set_full`.
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If asserts or exceptions are not enabled then undefined behaviour occurs.
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---
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```cpp
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size_t erase(const value_type& key)
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void erase(iterator i_element)
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void erase(iterator first, iterator last)
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```
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**Description**
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Erases values in the set.
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Iterators are not checked for validity.
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Since: 20.21.0
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```cpp
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template <typename K>
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size_t erase(K&& key)
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```
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**Description**
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Erases values in the map.
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---
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```cpp
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void clear()
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```
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**Description**
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Clears the lookup to a size of zero.
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## Search
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### find
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```cpp
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iterator find(const value_type& key)
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const_iterator find(const value_type& key) const
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```
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**Description**
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Finds the element that contains `key`, or `end()` if not found,
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```cpp
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template <typename K>
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iterator find(const K& key)
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const_iterator find(const K& key) const
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```
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**Description**
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Finds the element that contains `key`, or `end()` if not found,
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C++11 or above.
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For comparators that define `is_transparent`.
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Since: `20.21.0`
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### lower_bound
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```cpp
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iterator lower_bound(const value_type& key)
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const_iterator lower_bound(const value_type& key) const
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```
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**Description**
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Returns an iterator pointing to the first element in the container whose key is not considered to go before `key` (i.e., either it is equivalent or goes after).
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---
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Since: 20.21.0
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C++11 or above
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```cpp
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template <typename K>
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iterator lower_bound(const K& key)
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const_iterator lower_bound(const K& key) const
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```
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**Description**
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Returns an iterator pointing to the first element in the container whose key is not considered to go before `key` (i.e., either it is equivalent or goes after).
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C++11 or above.
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For comparators that define `is_transparent`.
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Since: `20.21.0`
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### upper_bound
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```cpp
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iterator upper_bound(const value_type& key)
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const_iterator upper_bound(const value_type& key) const
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```
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**Description**
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Returns an iterator pointing to the first element in the container whose key is considered to go after `key`.
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---
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```cpp
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template <typename K>
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iterator upper_bound(const K& key)
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const_iterator upper_bound(const K& key) const
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```
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**Description**
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Returns an iterator pointing to the first element in the container whose key is considered to go after `key`.
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C++11 or above.
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For comparators that define `is_transparent`.
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Since: `20.21.0`
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### equal_range
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```cpp
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ETL_OR_STD::pair<iterator, iterator> equal_range(const value_type& key)
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ETL_OR_STD::pair<const_iterator, const_iterator> equal_range(const value_type& key) const
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```
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**Description**
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Returns the bounds of a range that includes all the elements in the container which have a key equivalent to `key`.
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---
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```cpp
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template <typename K>
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pair<iterator, iterator> equal_range(const K& key)
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pair<const_iterator, const_iterator> equal_range(const K& key) const
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```
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**Description**
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Returns the bounds of a range that includes all the elements in the container which have a key equivalent to `key`.
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C++11 or above.
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For comparators that define `is_transparent`.
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Since: `20.21.0`
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### contains
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```cpp
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bool contains(const value_type& key) const
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```
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**Description**
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Check if the container contains the key.
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Since: 20.21.0
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C++11 or above
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For comparators that define is_transparent.
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```cpp
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template <typename K>
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bool contains(const K& k) const
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```
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**Description**
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Check if the container contains the key.
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Since: 20.21.0
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C++11 or above
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For comparators that define is_transparent.
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## Non-member functions
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Lexicographically comparisons
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```cpp
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operator ==
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```
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**Description**
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`true` if the contents of the maps are equal, otherwise `false`.
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---
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```cpp
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operator !=
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```
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**Description**
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`true` if the contents of the maps are not equal, otherwise `false`.
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## How it works
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Reference flat sets are different from the normal version in that the elements are not copied, but linked directly.
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This means that the lifetime of the element inserted must be as great as that of the set that contains it.
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Unlike most other reference containers, the set has a finite capacity.
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Flat sets are usually implemented internally as a sorted vector of values. Whilst this makes searching fast, it can have a detrimental effect when items are inserted into a container that stores complex, non-trivial values.
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As Inserting requires that all of the items above the insert position must be shifted, this can become an expensive operation for larger containers.
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To improve insertion performance ETL reference flat sets are implemented as vectors of pointers to values, sorted by value. An insertion will involve a copy of a range of pointers; an operation that can be made very fast.
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The downside is that access to an item via an iterator will involve one indirection and the overhead of the container will be one pointer per item. A normal flat set implementation does not have this overhead.
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