Template Class map_as_vector
Defined in File map_as_vector.h
Class Documentation
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template<typename KEY, typename VALUE, typename VECTOR_T = typename std::vector<std::pair<KEY, VALUE>>>
class map_as_vector A STL-like container which looks and behaves (almost exactly) like a std::map<> but is implemented as a linear std::vector<> indexed by KEY. Note that KEY must be integer types only (size_t, uint32_t, etc.) This implementation is much more efficient than std::map<> when the most common operation is accessing elements by KEY with find() or [], and the range of KEY values starts at 0 (or a reasonable low number).
This container is internally implemented as a linear array (std::vector) of the same fundamental type than the equivalent std::map<K,V>, that is, elements are
std::pair<K,V>(note that K is NOT const as in std::map). I know, I know… this implementation wastes a lot of useless key elements in the pair.first when indices are already implicit in the std::vector<> order… but I promise I’ll pay a beer to whoever show me an efficient alternative. If failed, update this comment: COUNTER OF WASTED HOURS WITH THIS: 3hNote that there is one fundamental difference wrt std::map<>: if you start with an empty map_as_vector<> and insert one element at the i’th position (with either [] or insert), the elements [0,i-1] will also exist then, but both their first & second entries (for the corresponding std::pair) will be undefined. This was intentional in order to gain efficiency (in particular, each std::pair<> doesn’t have a constructor when resizing the underlying std::vector).
The default underlying non-associative container is a “memory-aligned
std::vector<>”, but it can be changed to a standard vector<> or to a deque<> (to avoid memory reallocations) by changing the template parameter
VECTOR_T.Note
Defined in #include <mrpt/containers/map_as_vector.h>
Iterators stuff and other types
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using const_reverse_iterator = std::reverse_iterator<const_iterator>
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inline const_iterator begin() const
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inline const_iterator end() const
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inline reverse_iterator rbegin()
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inline const_reverse_iterator rbegin() const
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inline reverse_iterator rend()
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inline const_reverse_iterator rend() const
Constructors, read/write access and other operations
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map_as_vector() = default
< Default constructor - does nothing */
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inline size_t size() const
Copy constructor & operator= -> default
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inline bool empty() const
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inline size_type count(const key_type i) const
Count how many entries have a given key value - unlike std::map<K,V>, recall that this class will say an element i<N-1 exists just due to an insertion of element at N
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inline void clear()
Clear the contents of this container
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inline void swap(map_as_vector<KEY, VALUE> &o)
Efficient swap with another object
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inline VALUE &operator[](size_t i)
Write/read via [i] operator, that creates all elements up to (and including) the i’th if they didn’t exist already.
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inline const VALUE &at(size_t i) const
Read-only operator, throws exception if the given key index does not exist.
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inline VALUE &at(size_t i)
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
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inline void insert(const iterator &guess_point, const value_type &keyvalpair)
Insert pair<key,val>, as in std::map (guess_point is actually ignored in this class)
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inline void insert(const value_type &keyvalpair)
Insert pair<key,val>, as in std::map
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inline iterator find(size_t i)
Constant-time find, returning an iterator to the <key,val> pair or to end() if not found (that is, if it’s above the maximum index in the vector)
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inline const_iterator find(size_t i) const
Constant-time find, returning an iterator to the <key,val> pair or to end() if not found (that is, if it’s above the maximum index in the vector)
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using const_reverse_iterator = std::reverse_iterator<const_iterator>