deduction guides for std::deque

Since C++17

Header: <deque>

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

# Declarations

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)

template< ranges::input_range R,
class Alloc = std::allocator<ranges::range_value_t<R>> >
deque( std::from_range_t, R&&, Alloc = Alloc() )
-> deque<ranges::range_value_t<R>, Alloc>;

(since C++23)

# Notes

Feature-test macro Value Std Feature __cpp_lib_containers_ranges 202202L (C++23) Ranges-aware construction and insertion; overload (2)

# Example

#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()};
}