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Deduction guides

Deduction guides#

If possible, concurrent_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 Compare = std::less<iterator_key_t<InputIterator>>,
          typename Allocator = tbb_allocator<iterator_alloc_value_t<InputIterator>>>
concurrent_map( InputIterator, InputIterator,
                Compare = Compare(),
                Allocator = Allocator() )
-> concurrent_map<iterator_key_t<InputIterator>,
                  iterator_mapped_t<InputIterator>,
                  Compare,
                  Allocator>;

template <typename InputIterator,
          typename Allocator>
concurrent_map( InputIterator, InputIterator,
                Allocator )
-> concurrent_map<iterator_key_t<InputIterator>,
                  iterator_mapped_t<InputIterator>,
                  std::less<iterator_key_t<InputIterator>>,
                  Allocator>;

template <typename Key, typename T,
          typename Compare = std::less<std::remove_const_t<Key>>,
          typename Allocator = tbb_allocator<std::pair<const Key, T>>>
concurrent_map( std::initializer_list<std::pair<Key, T>>,
                Compare = Compare(),
                Allocator = Allocator() )
-> concurrent_map<std::remove_const_t<Key>,
                  T,
                  Compare,
                  Allocator>;

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

where the type aliases iterator_key_t, iterator_mapped_t, 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 Compare type does not meet the Allocator requirements.

Example

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

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

    // Deduces cm1 as concurrent_map<int, float>
    oneapi::tbb::concurrent_map cm1(v.begin(), v.end());

    // Deduces cm2 as concurrent_map<int, float>
    oneapi::tbb::concurrent_map cm2({std::pair(1, 2f), std::pair(2, 3f)});
}