20 General utilities library [utilities]

20.17 Class type_­index [type.index]

20.17.1 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>;
}

20.17.2 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.
  };
}
1
#
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.

20.17.3 type_­index members [type.index.members]

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type_index(const type_info& rhs) noexcept;
1
#
Effects: Constructs a type_­index object, the equivalent of target = &rhs.
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bool operator==(const type_index& rhs) const noexcept;
2
#
Returns: *target == *rhs.target.
🔗
bool operator<(const type_index& rhs) const noexcept;
3
#
Returns: target->before(*rhs.target).
🔗
bool operator>(const type_index& rhs) const noexcept;
4
#
Returns: rhs.target->before(*target).
🔗
bool operator<=(const type_index& rhs) const noexcept;
5
#
Returns: !rhs.target->before(*target).
🔗
bool operator>=(const type_index& rhs) const noexcept;
6
#
Returns: !target->before(*rhs.target).
🔗
strong_ordering operator<=>(const type_index& rhs) const noexcept;
7
#
Effects: Equivalent to: 
if (*target == *rhs.target) return strong_ordering::equal;
if (target->before(*rhs.target)) return strong_ordering::less;
return strong_ordering::greater;
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size_t hash_code() const noexcept;
8
#
Returns: target->hash_­code().
🔗
const char* name() const noexcept;
9
#
Returns: target->name().

20.17.4 Hash support [type.index.hash]

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template<> struct hash<type_index>;
1
#
For an object index of type type_­index, hash<type_­index>()(index) shall evaluate to the same result as index.hash_­code().