Deduction guides

If possible, concurrent_hash_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 HashCompare = tbb_hash_compare<iterator_key_t<InputIterator>>,
          typename Allocator = tbb_allocator<iterator_alloc_value_t<InputIterator>>>
concurrent_hash_map( InputIterator, InputIterator,
                     HashCompare = HashCompare(),
                     Allocator = Allocator() )
-> concurrent_hash_map<iterator_key_t<InputIterator>,
                       iterator_mapped_t<InputIterator>,
                       HashCompare,
                       Allocator>;

template <typename InputIterator,
          typename Allocator>
concurrent_hash_map( InputIterator, InputIterator, Allocator )
-> concurrent_hash_map<iterator_key_t<InputIterator>,
                       iterator_mapped_t<InputIterator>,
                       tbb_hash_compare<iterator_key_t<InputIterator>>,
                       Allocator>;

template <typename Key, typename T,
          typename HashCompare = tbb_hash_compare<std::remove_const_t<Key>>,
          typename Allocator = tbb_allocator<std::pair<const Key, T>>>
concurrent_hash_map( std::initializer_list<std::pair<Key, T>>,
                     HashCompare = HashCompare(),
                     Allocator = Allocator() )
-> concurrent_hash_map<std::remove_const_t<Key>,
                       T,
                       HashCompare,
                       Allocator>;

template <typename Key, typename T,
          typename Allocator>
concurrent_hash_map( std::initializer_list<std::pair<Key, T>>,
                     Allocator )
-> concurrent_hash_map<std::remove_const_t<Key>,
                       T,
                       tbb_hash_compare<std::remove_const_t<Key>>,
                       Allocator>;

Where 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 HashCompare type does not meet the Allocator requirements.

Example

#include <oneapi/tbb/concurrent_hash_map.h>
#include <vector>

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

    // Deduces chmap1 as oneapi::tbb::concurrent_hash_map<int, float>
    oneapi::tbb::concurrent_hash_map chmap1(v.begin(), v.end());

    std::allocator<std::pair<const int, float>> alloc;
    // Deduces chmap2 as oneapi::tbb::concurrent_hash_map<int, float,
    //                                            tbb_hash_compare<int>,
    //                                            std::allocator<std::pair<const int, float>>>
    oneapi::tbb::concurrent_hash_map chmap2(v.begin(), v.end(), alloc);
}