deduction guides for std::priority_queue

The following deduction guides are provided for std::priority_queue :

These overloads participate in overload resolution only if

• InputIt satisfies LegacyInputIterator,
• Comp does not satisfy Allocator,
• Container does not satisfy Allocator,
• for overloads (4,5),(since C++23) Alloc satisfies Allocator, and
• for overloads (3,6), std::uses_allocator_v <Container, Alloc> is true.

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.

[edit] Notes

[edit] Example

#include <functional>
#include <iostream>
#include <queue>
#include <vector>
 
int main()
{
 const std::vector <int> v = {1, 2, 3, 4};
 std::priority_queue pq1{std::greater <int>{}, v}; // deduces std::priority_queue<
 // int, std::vector<int>,
 // std::greater<int>>
 for (; !pq1.empty(); pq1.pop())
 std::cout << pq1.top() << ' ';
 std::cout << '\n';
 
 std::priority_queue pq2{v.begin(), v.end()}; // deduces std::priority_queue<int>
 
 for (; !pq2.empty(); pq2.pop())
 std::cout << pq2.top() << ' ';
 std::cout << '\n';
}

1 2 3 4
4 3 2 1

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

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