deduction guides for std::queue

template< class Container >
queue( Container )
  -> queue<typename Container::value_type, Container>;

template< class InputIt >
queue( InputIt, InputIt )
  -> queue<typename std::iterator_traits<InputIt>::value_type>;

template< class Container, class Alloc > 
queue( Container, Alloc )
  -> queue<typename Container::value_type, Container>;

template< class InputIt, class Alloc >
queue( InputIt, InputIt, Alloc )
  -> queue<typename std::iterator_traits<InputIt>::value_type,
    std::deque<typename std::iterator_traits<InputIt>::value_type, Alloc>>;

These deduction guides are provided for queue to allow deduction from underlying container type.

These overloads participate in overload resolution only if.

• InputIt (if exists) satisfies LegacyInputIterator,
• Container (if exists) does not satisfy Allocator,
• for (3) (until C++23)(4) (since C++23), Alloc satisfies Allocator, and
• std::uses_allocator_v<Container, Alloc> is true if both Container and Alloc exist.

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

#include <vector>
#include <queue>
int main() {
   std::vector<int> v = {1,2,3,4};
   std::queue s{v};    // guide #1 deduces std::queue<int, vector<int>>
}