c8bc1bd896
* Corrected the documented make_xxx factory signatures and examples
The Make template sections across the container documentation had
drifted from the implementations, largely through copy-paste:
- map.md, multimap.md and flat-multimap.md all documented
make_flat_map; multiset.md documented make_set; flat-multiset.md
documented make_flat_set; unordered-multimap.md documented
make_unordered_map. Names and examples now match each container.
- Every signature omitted the C++11-required trailing return type
despite the sections being labelled C++11 and above; several also
used a parameter name (TValues) that did not match any template
parameter, and the unordered map headers were missing a comma.
- forward-list.md documented a make_array-style signature with an
explicit element type; the real function deduces the element type as
the common type of the arguments, as documented for make_list.
- The flat_set/flat_multiset template headers were missing the
variadic parameter pack, and their examples passed a braced list to
a variadic function, which does not compile; set.md used TKeyCompare
where the implementation uses TCompare.
- deque.md and the reference container docs were missing code fences.
- Updated the four reference_flat_* function. However these functions
cannot be instantiated at all (the reference containers have no
initializer_list constructor, since one would dangle by design), so
the documented examples have never compiled.
Every remaining documented example verified to compile with clang 22
(C++17) against the current headers.
* Fixed C++17-only syntax in factory examples and flagged the non-compilable ones
Review feedback on the make_xxx documentation examples:
- All the map-family factory examples are labelled C++11 and above but
constructed their pairs with class template argument deduction
(etl::pair{0, 1}), which requires C++17. The pairs in the make_flat_map,
make_flat_multimap, make_map, make_multimap, make_unordered_map,
make_unordered_multimap, make_reference_flat_map and
make_reference_flat_multimap examples now name their template arguments
explicitly. The template deduction guide examples are unchanged, as
those sections are labelled C++17 and above. Verified with clang 22 in
C++14 mode, which, like C++11, has no deduction guides.
- The four make_reference_flat_* examples are now preceded by a warning
callout stating that they do not currently compile: the functions
cannot be instantiated because the reference containers have no
initializer_list constructor. The examples themselves are retained,
rewritten to pass named lvalues rather than temporaries, since the
reference containers store references to external objects and the
temporaries would dangle even if the functions compiled. The defect
is being reported separately.
---------
Co-authored-by: John Wellbelove <jwellbelove@users.noreply.github.com>
11 KiB
| title |
|---|
| reference_flat_multimap |
{{< callout type="info">}}
Header: reference_flat_multimap.h
Similar to: std::reference_flat_multimap
{{< /callout >}}
A fixed capacity reference map 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.
Uses etl::less as the default key comparison method.
etl::reference_flat_multimap<typename TKey, typename TMapped, const size_t SIZE, TKeyCompare = less>
Inherits from etl::ireference_flat_multimap<TKey, TMapped, TKeyCompare>.
etl::ireference_flat_multimap may be used as a size independent pointer or reference type for any etl::reference_flat_multimap instance.
Template deduction guides
C++17 and above
template <typename... TPairs>
etl::reference_flat_multimap(TPairs...)
Example
etl::reference_flat_multimap data{ etl::pair{0, 1}, etl::pair{2, 3}, etl::pair{4, 5}, etl::pair{6, 7} };
Defines data as an reference_flat_multimap of int, of length 4, containing the supplied data.
Make template
C++11 and above
template <typename TKey,
typename TMapped,
typename TKeyCompare = etl::less<TKey>,
typename... TPairs>
constexpr auto make_reference_flat_multimap(TPairs&&... pairs) -> etl::reference_flat_multimap<TKey, TMapped, sizeof...(TPairs), TKeyCompare>
Example
{{< callout type="warning" >}}
This example does not currently compile: make_reference_flat_multimap cannot be
instantiated, because the reference containers have no initializer_list
constructor for its braced return value to bind to. This is a known defect.
{{< /callout >}}
// The referenced objects must outlive the container.
etl::pair<int, int> p0{0, 1};
etl::pair<int, int> p1{2, 3};
etl::pair<int, int> p2{4, 5};
etl::pair<int, int> p3{6, 7};
auto data = etl::make_reference_flat_multimap<int, int>(p0, p1, p2, p3);
Member types
key_type TKey
mapped_type TMapped
value_type pair<key_type, mapped_type>
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<iterator>
const_reverse_iterator ETL_OR_STD::reverse_iterator<const_iterator>
Constructor
etl::reference_flat_multimap<Tkey, TMapped, SIZE, TKeyCompare>()
Description
Default constructor.
etl::reference_flat_multimap(const flat_map& other)
Description
Copy constructor.
template <typename TIterator>
etl::reference_flat_multimap<Tkey, TMapped, SIZE, TKeyCompare>(TIterator begin, TIterator end)
Description
If the map is full then raises an etl::reference_flat_map_full.
If asserts or exceptions are not enabled then undefined behaviour occurs.
Element access
at
TMapped& at(const key_type& key)
const TMapped& at(const key_type& key) const
Description
Returns a reference or const reference to the indexed element.
Raises an etl::flat_map_out_of_range if the key is not in the table.
If asserts or exceptions are not enabled then undefined behaviour occurs.
template <typename K, typename KC = TKeyCompare>
mapped_type& at(const K& key)
const mapped_type& at(const K& key) const
Description
Returns a reference or const reference to the indexed element.
Raises an etl::flat_map_out_of_range if the key is not in the table.
If asserts or exceptions are not enabled then undefined behaviour occurs.
C++11 or above.
For comparators that define is_transparent.
Since: 20.21.0
find
template <typename K>
iterator find(const key_type& key)
const_iterator find(const key_type& key) const
Description
Returns a reference or const reference to the indexed element.
Raises an etl::flat_map_out_of_range if the key is not in the table.
If asserts or exceptions are not enabled then undefined behaviour occurs.
template <typename K>
iterator find(const K& key)
const_iterator find(const K& key) const
Description
Returns a reference or const reference to the indexed element.
Raises an etl::flat_map_out_of_range if the key is not in the table.
If asserts or exceptions are not enabled then undefined behaviour occurs.
C++11 or above.
For comparators that define is_transparent.
Since: 20.21.0
lower_bound
iterator lower_bound(const key_type& key)
const_iterator lower_bound(const key_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).
template <typename K, typename KC = TKeyCompare>
iterator lower_bound(const K& key)
const_iterator lower_bound(const K& key) const
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
iterator upper_bound(const key_type& key)
const_iterator upper_bound(const key_type& key) const
Description
Returns an iterator pointing to the first element in the container whose key is considered to go after key.
template <typename K, typename KC = TKeyCompare>
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
pair<iterator, iterator> equal_range(const key_type& key)
pair<const_iterator, const_iterator> equal_range(const key_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.
C++11 or above.
For comparators that define is_transparent.
Since: 20.21.0
template <typename K, typename KC = TKeyCompare>
pair<iterator, iterator> equal_range(const K& key)
pair<const_iterator, const_iterator> 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
bool contains(const value_type& key) const
Description
Check if the container contains the key.
Since: 20.21.0
template <typename K, typename KC = TKeyCompare>
bool contains(const K& k) const
Description
Check if the container contains the key.
C++11 or above.
For comparators that define is_transparent.
Since: 20.21.0
Iterators
iterator begin()
const_iterator begin() const
const_iterator cbegin() const
Description
Returns an iterator to the beginning of the map.
iterator end()
const_iterator end() const
const_iterator cend() const
Description
Returns an iterator to the end of the map.
iterator rbegin()
const_iterator rbegin() const
const_iterator crbegin() const
Description
Returns a reverse iterator to the beginning of the map.
iterator rend()
const_iterator rend() const
const_iterator crend() const
Description
Returns a reverse iterator to the end of the map.
Capacity
bool empty() const
Description
Returns true if the size of the map is zero, otherwise false.
bool full() const
Description
Returns true if the size of the lookup is SIZE, otherwise false.
size_t size() const
Description
Returns the size of the lookup.
size_t max_size() const
Description
Returns the maximum possible size of the map.
size_t available() const
Description
Returns the remaining available capacity in the map.
Modifiers
reference_flat_multimap& operator = (const reference_flat_multimap& rhs)
Description
Copies the data from another flat map.
pair<iterator, bool> insert(const value_type& value)
Description
Inserts value into the map.
iterator insert(iterator position, const value_type& value)
Description
Inserts value into the map at th esuggested position.
template <typename TIterator>
void insert(TIterator first, TIterator last)
Description
Inserts values in to the map. If the map is full then raises an etl::flat_map_full.
If asserts or exceptions are not enabled then undefined behaviour occurs.
size_t erase(const key_type& key)
Description
Erase the element with key.
void erase(iterator i_element)
Description
Erase the element at i_element.
void erase(iterator first, iterator last)
Description
Erase elements in the range [first, last).
template <typename K>
size_t erase(K&& key)
Description
Erases values in the map.
Since: 20.21.0
void clear()
Description
Clears the lookup to a size of zero.
Iterator are not checked for validity.
Non-member functions
Lexicographically comparisons
operator ==
Description
true if the contents of the maps are equal, otherwise false.
operator !=
Description
true if the contents of the maps are not equal, otherwise false.
Technical stuff
Reference flat maps 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 map that contains it.
Unlike most other reference containers, the map has a finite capacity.
Flat maps are usually implemented internally as a sorted vector of key/value pairs. Whilst this makes searching fast, it can have a detrimental effect when items are inserted into a container that stores complex, non-trivial keys or 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 maps are implemented as vectors of pointers to key/value pairs, sorted by key 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 map implementation does not have this overhead.