# deduction guides for `std::set`

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< cpp‎ | container‎ | set

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.

### Notes

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

### 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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