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deduction guides for std::set

From cppreference.com
< cpp‎ | container‎ | set
 
 
 
std::set
Member functions
          
 
Defined in header <set>
template<

    class InputIt,
    class Comp = std::less <typename std::iterator_traits <InputIt>::value_type>,
    class Alloc = std::allocator <typename std::iterator_traits <InputIt>::value_type>>
set( InputIt, InputIt, Comp = Comp(), Alloc = Alloc() )

    -> set<typename std::iterator_traits <InputIt>::value_type, Comp, Alloc>;
(1) (since C++17)
template<

    class Key, class Comp = std::less <Key>,
    class Alloc = std::allocator <Key> >
set( std::initializer_list <Key>, Comp = Comp(), Alloc = Alloc() )

    -> set<Key, Comp, Alloc>;
(2) (since C++17)
template< class InputIt, class Alloc >

set( InputIt, InputIt, Alloc )
    -> set<typename std::iterator_traits <InputIt>::value_type,

           std::less <typename std::iterator_traits <InputIt>::value_type>, Alloc>;
(3) (since C++17)
template< class Key, class Alloc >

set( std::initializer_list <Key>, Alloc )

    -> set<Key, std::less <Key>, Alloc>;
(4) (since C++17)
template< ranges::input_range R, class Compare = less<ranges::range_value_t <R>>,

          class Alloc = std::allocator <ranges::range_value_t <R>> >
set( std::from_range_t, R&&, Compare = Compare(), Alloc = Alloc() )

    -> set<ranges::range_value_t <R>, Compare, Alloc>;
(5) (since C++23)
template< ranges::input_range R, class Alloc >

set( std::from_range_t, R&&, Alloc )

    -> set<ranges::range_value_t <R>, std::less <ranges::range_value_t <R>>, Alloc>;
(6) (since C++23)
1-4) These deduction guides are provided for set to allow deduction from an iterator range (overloads (1,3)) and std::initializer_list (overloads (2,4)).
5,6) These deduction guides are provided for set to allow deduction from a std::from_range_t tag and an input_range.

These overloads participate in overload resolution only if InputIt satisfies LegacyInputIterator, Alloc satisfies Allocator, and Comp does not satisfy Allocator.

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

Feature-test macro Value Std Feature
__cpp_lib_containers_ranges 202202L (C++23) Ranges-aware construction and insertion; overload (5,6)

[edit] Example

Run this code
#include <set>
 
int main()
{
 // guide #2 deduces std::set<int>
 std::set s = {1, 2, 3, 4};
 
 // guide #1 deduces std::set<int>
 std::set s2(s.begin(), s.end());
}

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