# Deduction guides

If possible, `concurrent_bounded_queue` 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 guide is provided:

    template <typename InputIterator,
              typename Allocator = tbb::cache_aligned_allocator<iterator_value_t<InputIterator>>
    concurrent_bounded_queue( InputIterator, InputIterator,
                              Allocator = Allocator() )
    -> concurrent_bounded_queue<iterator_value_t<InputIterator>,
                                Allocator>;

Where the type alias `iterator_value_t` is defined as follows:

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

This 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.

Example

    #include <oneapi/tbb/concurrent_queue.h>
    #include <vector>
    #include <memory>

    int main() {
        std::vector<int> vec;

        // Deduces cq1 as oneapi::tbb::concurrent_bounded_queue<int>
        oneapi::tbb::concurrent_bounded_queue cq1(vec.begin(), vec.end());

        // Deduces cq2 as oneapi::tbb::concurrent_bounded_queue<int, std::allocator<int>>
        oneapi::tbb::concurrent_bounded_queue cq2(vec.begin(), vec.end(), std::allocator<int>{})
    }