deduction guides for std::queue

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
• std::uses_allocator_v<Container, Alloc> is true if both Container and Alloc

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 { } )

Notes

Example

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