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