22 General utilities library [utilities]

22.11 Class type_index [type.index]

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

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#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]

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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. }; }
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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]

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

22.11.4 Hash support [type.index.hash]

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