17 Language support library [support] (original) (raw)

17.7 Type identification [support.rtti]

17.7.1 General [support.rtti.general]

The header defines a type associated with type information generated by the implementation.

It also defines two types for reporting dynamic type identification errors.

The header defines a wrapper type for use as an index type in associative containers ([associative]) and in unordered associative containers ([unord]).

17.7.3 Class type_info [type.info]

namespace std { class type_info { public: virtual ~type_info();constexpr bool operator==(const type_info& rhs) const noexcept;bool before(const type_info& rhs) const noexcept; size_t hash_code() const noexcept;const char* name() const noexcept; type_info(const type_info&) = delete; type_info& operator=(const type_info&) = delete;};}

The classtype_infodescribes type information generated by the implementation ([expr.typeid]).

Objects of this class effectively store a pointer to a name for the type, and an encoded value suitable for comparing two types for equality or collating order.

The names, encoding rule, and collating sequence for types are all unspecifiedand may differ between programs.

constexpr bool operator==(const type_info& rhs) const noexcept;

Effects: Compares the current object with rhs.

Returns: trueif the two values describe the same type.

bool before(const type_info& rhs) const noexcept;

Effects: Compares the current object with rhs.

Returns: trueif*thisprecedes rhs in the implementation's collation order.

size_t hash_code() const noexcept;

Returns: An unspecified value, except that within a single execution of the program, it shall return the same value for any two type_infoobjects which compare equal.

Remarks: An implementation should return different values for twotype_info objects which do not compare equal.

const char* name() const noexcept;

Returns: An implementation-defined ntbs.

17.7.4 Class bad_cast [bad.cast]

namespace std { class bad_cast : public exception { public: constexpr const char* what() const noexcept override;};}

The classbad_castdefines the type of objects thrown as exceptions by the implementation to report the execution of an invaliddynamic_castexpression ([expr.dynamic.cast]).

constexpr const char* what() const noexcept override;

Returns: An implementation-defined ntbs.

17.7.5 Class bad_typeid [bad.typeid]

namespace std { class bad_typeid : public exception { public: constexpr const char* what() const noexcept override;};}

The classbad_typeiddefines the type of objects thrown as exceptions by the implementation to report a null pointer in atypeidexpression ([expr.typeid]).

constexpr const char* what() const noexcept override;

Returns: An implementation-defined ntbs.

17.7.7 Class type_index [type.index]

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; };}

The class type_index provides a simple wrapper fortype_info which can be used as an index type in associative containers ([associative]) and in unordered associative containers ([unord]).

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;

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().