deductionguidesforstd::set(3)

NAME
deductionguidesforstd::set - deductionguidesforstd::set

Synopsis
   Defined in header <set>
   template<class InputIt,
   class Comp = std::less<typename
   std::iterator_traits<InputIt>::value_type>,
   class Alloc = std::allocator<typename (1) (since C++17)
   std::iterator_traits<InputIt>::value_type>>
   set(InputIt, InputIt, Comp = Comp(), Alloc = Alloc())
   -> set<typename std::iterator_traits<InputIt>::value_type, Comp,
   Alloc>;
   template<class Key, class Comp = std::less<Key>, class Alloc =
   std::allocator<Key>>
                        (2) (since C++17)
   set(std::initializer_list<Key>, Comp = Comp(), Alloc = Alloc())
   -> set<Key, Comp, Alloc>;
   template<class InputIt, class Alloc>
   set(InputIt, InputIt, Alloc)
   -> set<typename std::iterator_traits<InputIt>::value_type, (3) (since C++17)
   std::less<typename std::iterator_traits<InputIt>::value_type>,
   Alloc>;
   template<class Key, class Alloc>
   set(std::initializer_list<Key>, Alloc) (4) (since C++17)
   -> set<Key, std::less<Key>, Alloc>;
   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
   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.

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>
 }