A C++ template library for embedded applications
Designed and maintained by
Aster Consulting Ltd



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 std::less as the default key comparison method.

etl::reference_flat_set<typename T, const size_t SIZE, TCompare = std::less>

Inherits from etl::ireference_flat_set<T, TCompare>
etl::ireference_flat_set may be used as a size independent pointer or reference type for any
etl::reference_flat_set instance.

Member types

key_type                T
value_type              T
size_type               std::size_t
difference_type         std::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        std::reverse_iterator<iterator>
const_reverse_iterator  std::reverse_iterator<const_iterator>


etl::flat_set<T, SIZE, TCompare>();

etl::flat_set(const flat_set& other)

template <typename TIterator>
etl::flat_set<T, SIZE, TCompare>(TIterator begin, TIterator end);
If the set is full then emits an etl::reference_flat_set_full. If asserts or exceptions are not enabled then undefined
behaviour occurs.


iterator begin()
const_iterator begin() const
const_iterator cbegin() const
Returns an iterator to the beginning of the set.

iterator end()
const_iterator end() const
const_iterator cend() const
Returns an iterator to the end of the set.

iterator rbegin()
const_iterator rbegin() const
const_iterator crbegin() const
Returns a reverse iterator to the beginning of the set.

iterator rend()
const_iterator rend() const
const_iterator crend() const
Returns a reverse iterator to the end of the set.


bool empty() const
Returns true if the size of the set is zero, otherwise false.

bool full() const
Returns true if the size of the lookup is SIZE, otherwise false.

size_t size() const
Returns the size of the lookup.

size_t max_size() const
Returns the maximum possible size of the set.

size_t available() const
Returns the remaining available capacity in the set.


flat_set& operator = (const flat_set& rhs)
Copies the data from another flat set.

std::pair<iterator, bool> insert(const value_type& value)
iterator insert(iterator position, const value_type& value)
template <class TIterator>
void insert(TIterator first, TIterator last)
Inserts values in to the set.
If the set is full then emits an etl::reference_flat_set_full. If asserts or exceptions are not enabled then undefined
behaviour occurs.

size_t erase(key_value_parameter_t key)
void erase(iterator i_element)
void erase(iterator first, iterator last)
Erases values in the set.
Iterators are not checked for validity.

void clear();
Clears the lookup to a size of zero.


iterator find(key_value_parameter_t key)
const_iterator find(key_value_parameter_t key) const

iterator lower_bound(key_value_parameter_t key)
const_iterator lower_bound(key_value_parameter_t key) const

iterator upper_bound(key_value_parameter_t key)
const_iterator upper_bound(key_value_parameter_t key) const

std::pair<iterator, iterator> equal_range(key_value_parameter_t key)
std::pair<const_iterator, const_iterator> equal_range(key_value_parameter_t key) const

Non-member functions

Lexicographically comparisons

==  true if the contents of the sets are equal, otherwise false.
!=  true if the contents of the sets are not equal, otherwise false.

Technical stuff

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.
intrusive_flat_set.h / reference_flat_multiset.h