22 General utilities library [utilities]

22.11 Class type_­index [type.index]

22.11.1 Header <typeindex> synopsis [type.index.synopsis]

#include <compare> // see [compare.syn] namespace std { class type_index; template<class T> struct hash; template<> struct hash<type_index>; }

22.11.2 type_­index overview [type.index.overview]

namespace std { class type_index { public: type_index(const type_info& rhs) noexcept; bool operator==(const type_index& rhs) const noexcept; bool operator< (const type_index& rhs) const noexcept; bool operator> (const type_index& rhs) const noexcept; bool operator<=(const type_index& rhs) const noexcept; bool operator>=(const type_index& rhs) const noexcept; strong_ordering operator<=>(const type_index& rhs) const noexcept; size_t hash_code() const noexcept; const char* name() const noexcept; private: const type_info* target; // exposition only // Note that the use of a pointer here, rather than a reference, // means that the default copy/move constructor and assignment // operators will be provided and work as expected. }; }
The class type_­index provides a simple wrapper for type_­info which can be used as an index type in associative containers and in unordered associative containers.

22.11.3 type_­index members [type.index.members]

type_index(const type_info& rhs) noexcept;
Effects: Constructs a type_­index object, the equivalent of target = &rhs.
bool operator==(const type_index& rhs) const noexcept;
Returns: *target == *rhs.target.
bool operator<(const type_index& rhs) const noexcept;
Returns: target->before(*rhs.target).
bool operator>(const type_index& rhs) const noexcept;
Returns: rhs.target->before(*target).
bool operator<=(const type_index& rhs) const noexcept;
Returns: !rhs.target->before(*target).
bool operator>=(const type_index& rhs) const noexcept;
Returns: !target->before(*rhs.target).
strong_ordering operator<=>(const type_index& rhs) const noexcept;
Effects: Equivalent to: if (*target == *rhs.target) return strong_ordering::equal; if (target->before(*rhs.target)) return strong_ordering::less; return strong_ordering::greater;
size_t hash_code() const noexcept;
Returns: target->hash_­code().
const char* name() const noexcept;
Returns: target->name().

22.11.4 Hash support [type.index.hash]

template<> struct hash<type_index>;
For an object index of type type_­index, hash<type_­index>()(index) shall evaluate to the same result as index.hash_­code().