deduction guides for std::stack

These deduction guides are provided for stack 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.

Notes

Example

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