deductionguidesforstd::unordered_set (3) - Linux Manuals

deductionguidesforstd::unordered_set: deductionguidesforstd::unordered_set

NAME

deductionguidesforstd::unordered_set - deductionguidesforstd::unordered_set

Synopsis

Defined in header <unordered_set>
template<class InputIt,
class Hash = std::hash<typename std::iterator_traits<InputIt>::value_type>,
class Pred = std::equal_to<typename std::iterator_traits<InputIt>::value_type>,
class Alloc = std::allocator<typename std::iterator_traits<InputIt>::value_type>> (1) (since C++17)
unordered_set(InputIt, InputIt,
typename /*see below*/::size_type = /*see below*/,
Hash = Hash(), Pred = Pred(), Alloc = Alloc())
-> unordered_set<typename std::iterator_traits<InputIt>::value_type, Hash, Pred, Alloc>;
template<class T,
class Hash = std::hash<T>,
class Pred = std::equal_to<T>,
class Alloc = std::allocator<T>> (2) (since C++17)
unordered_set(std::initializer_list<T>,
typename /*see below*/::size_type = /*see below*/,
Hash = Hash(), Pred = Pred(), Alloc = Alloc())
-> unordered_set<T, Hash, Pred, Alloc>;
template<class InputIt, class Alloc>
unordered_set(InputIt, InputIt, typename /*see below*/::size_type, Alloc)
-> unordered_set<typename std::iterator_traits<InputIt>::value_type, (3) (since C++17)
std::hash<typename std::iterator_traits<InputIt>::value_type>,
std::equal_to<typename std::iterator_traits<InputIt>::value_type>,
Alloc>;
template<class InputIt, class Hash, class Alloc>
unordered_set(InputIt, InputIt, typename /*see below*/::size_type, Hash, Alloc) (4) (since C++17)
-> unordered_set<typename std::iterator_traits<InputIt>::value_type, Hash,
std::equal_to<typename std::iterator_traits<InputIt>::value_type>, Allocator>;
template<class T, class Allocator>
unordered_set(std::initializer_list<T>, typename /*see below*/::size_type, Allocator) (5) (since C++17)
-> unordered_set<T, std::hash<T>, std::equal_to<T>, Alloc>;
template<class T, class Hash, class Alloc>
unordered_set(std::initializer_list<T>, typename /*see below*/::size_type, Hash, Alloc) (6) (since C++17)
-> unordered_set<T, Hash, std::equal_to<T>, Alloc>;

These deduction_guides are provided for unordered_set to allow deduction from an iterator range (overloads (1,3,4)) and std::initializer_list (overloads (2,5.6)). This overload only participates in overload resolution if InputIt satisfies LegacyInputIterator, Alloc satisfies Allocator, neither Hash nor Pred satisfy Allocator, Hash is not an integral type
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.
The size_type parameter type in these guides refers to the size_type member type of the type deduced by the deduction guide.

Example

// Run this code

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