Deduction guides¶

If possible, concurrent_unordered_map constructors support class template argument deduction (since C++17). Copy and move constructors, including constructors with an explicit allocator_type argument, provide implicitly-generated deduction guides. In addition, the following explicit deduction guides are provided:

template <typename InputIterator,
          typename Hash = std::hash<iterator_key_t<InputIterator>>,
          typename KeyEqual = std::equal_to<iterator_key_t<InputIterator>>,
          typename Allocator = tbb::tbb_allocator<iterator_alloc_value_t<InputIterator>>>
concurrent_unordered_map( InputIterator, InputIterator,
                          map_size_type = {},
                          Hash = Hash(),
                          KeyEqual = KeyEqual(),
                          Allocator = Allocator() )
-> concurrent_unordered_map<iterator_key_t<InputIterator>,
                            iterator_mapped_t<InputIterator>,
                            Hash,
                            KeyEqual,
                            Allocator>;

template <typename InputIterator,
          typename Hash,
          typename Allocator>
concurrent_unordered_map( InputIterator, InputIterator,
                          map_size_type,
                          Hash,
                          Allocator )
-> concurrent_unordered_map<iterator_key_t<InputIterator>,
                            iterator_mapped_t<InputIterator>,
                            Hash,
                            std::equal_to<iterator_key_t<InputIterator>>,
                            Allocator>;

template <typename InputIterator,
          typename Allocator>
concurrent_unordered_map( InputIterator, InputIterator,
                          map_size_type,
                          Allocator )
-> concurrent_unordered_map<iterator_key_t<InputIterator>,
                            iterator_mapped_t<InputIterator>,
                            std::hash<iterator_key_t<InputIterator>>,
                            std::equal_to<iterator_key_t<InputIterator>>,
                            Allocator>;

template <typename Key,
          typename T,
          typename Hash = std::hash<std::remove_const_t<Key>>,
          typename KeyEqual = std::equal_to<std::remove_const_t<Key>>,
          typename Allocator = tbb::tbb_allocator<std::pair<const Key, T>>>
concurrent_unordered_map( std::initializer_list<std::pair<Key, T>>,
                          map_size_type = {},
                          Hash = Hash(),
                          KeyEqual = KeyEqual(),
                          Allocator = Allocator() )
-> concurrent_unordered_map<std::remove_const_t<Key>,
                            T,
                            Hash,
                            KeyEqual,
                            Allocator>;

template <typename Key,
          typename T,
          typename Allocator>
concurrent_unordered_map( std::initializer_list<std::pair<Key, T>>,
                          map_size_type,
                          Allocator )
-> concurrent_unordered_map<std::remove_const_t<Key>,
                            T,
                            std::hash<std::remove_const_t<Key>>,
                            std::equal_to<std::remove_const_t<Key>>,
                            Allocator>;

template <typename Key,
          typename T,
          typename Allocator>
concurrent_unordered_map( std::initializer_list<std::pair<Key, T>>,
                          Allocator )
-> concurrent_unordered_map<std::remove_const_t<Key>,
                            T,
                            std::hash<std::remove_const_t<Key>>,
                            std::equal_to<std::remove_const_t<Key>>,
                            Allocator>;

template <typename Key,
          typename T,
          typename Hash,
          typename Allocator>
concurrent_unordered_map( std::initializer_list<std::pair<Key, T>>,
                          map_size_type,
                          Hash,
                          Allocator )
-> concurrent_unordered_map<std::remove_const_t<Key>,
                            T,
                            Hash,
                            std::equal_to<std::remove_const_t<Key>>,
                            Allocator>;

Where the map_size_type type refers to the size_type member type of the deduced concurrent_unordered_map and the type aliases iterator_key_t, iterator_mapped_t, and iterator_alloc_value_t are defined as follows:

template <typename InputIterator>
using iterator_key_t = std::remove_const_t<typename std::iterator_traits<InputIterator>::value_type::first_type>;

template <typename InputIterator>
using iterator_mapped_t = typename std::iterator_traits<InputIterator>::value_type::second_type;

template <typename InputIterator>
using iterator_alloc_value_t = std::pair<std::add_const_t<iterator_key_t<InputIterator>,
                                         iterator_mapped_t<InputIterator>>>;

These deduction guides only participate in the overload resolution if the following requirements are met:

The InputIterator type meets the InputIterator requirements described in the [input.iterators] section of the ISO C++ Standard.
The Allocator type meets the Allocator requirements described in the [allocator.requirements] section of the ISO C++ Standard.
The Hash type does not meet the Allocator requirements.
The KeyEqual type does not meet the Allocator requirements.

Example

#include <oneapi/tbb/concurrent_unordered_map.h>
#include <vector>
#include <functional>

struct CustomHasher {...};

int main() {
    std::vector<std::pair<int, float>> v;

    // Deduces m1 as concurrent_unordered_map<int, float>
    oneapi::tbb::concurrent_unordered_map m1(v.begin(), v.end());

    // Deduces m2 as concurrent_unordered_map<int, float, CustomHasher>;
    oneapi::tbb::concurrent_unordered_map m2(v.begin(), v.end(), CustomHasher{});
}

oneAPI Specification 1.1-rev-1 documentation

Deduction guides¶