# 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)

These deduction guides are provided for set to allow deduction from an iterator range (overloads (1,3)) and std::initializer_list (overloads (2,4)). These overloads only participate in overload resolution 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.

### Example

Run this code

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

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