# deduction guides for `std::deque`

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< cpp‎ | container‎ | deque

Defined in header `<deque>` |  |
template< class InputIt, class Alloc = std::allocator<typename std::iterator_traits<InputIt>::value_type>> deque(InputIt, InputIt, Alloc = Alloc()) -> deque<typename std::iterator_traits<InputIt>::value_type, Alloc>; |  | (since C++17)

This deduction guide is provided for deque to allow deduction from an iterator range. This overload only participates in overload resolution if `InputIt` satisfies LegacyInputIterator and `Alloc` satisfies Allocator.

Note: the extent to which the library determines that a type does not satisfy LegacyInputIterator is unspecified, except that as a minimum integral types do not qualify as input iterators. Likewise, the extent to which it determines that a type does not satisfy Allocator is unspecified, except that as a minimum the member type `Alloc::value_type` must exist and the expression std::declval<Alloc&>().allocate(std::size_t{}) must be well-formed when treated as an unevaluated operand.

### Example

Run this code

    #include <deque>
    #include <vector>
    int main() {
       std::vector<int> v = {1, 2, 3, 4};

       // uses explicit deduction guide to deduce std::deque<int>
       std::deque x(v.begin(), v.end());

       // deduces std::deque<std::vector<int>::iterator>
       // first phase of overload resolution for list-initialization selects the candidate
       // synthesized from the initializer-list constructor; second phase is not performed and
       // deduction guide has no effect
       std::deque y{v.begin(), v.end()};
    }

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