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Added docs for std::hash

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But I do not know if they copile with QuickBook.
This commit is contained in:
Andrzej Krzemienski
2022-05-23 21:00:00 +02:00
parent 52abe4842e
commit ec677383dc
4 changed files with 50 additions and 2 deletions
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34
doc/28_ref_optional_semantics.qbk
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@ -1408,3 +1408,37 @@ assert (addressof(*opt0) == addressof(y));
``
[endsect]
[section Detailed Semantics - std::hash Specializations]
__SPACE__
[#reference_std_hash_spec]
``
namespace std {
template <typename T>
struct hash<boost::optional<T> > ;
template <typename T>
struct hash<boost::optional<T&> > ;
} // namespace std
``
The specialization `hash<optional<T>>`` is enabled if and only if
`hash<remove_­const_­t<T>> is enabled. When enabled, for an object `o`
of type `optional<T>``, if `o.has_­value() == true`, then `hash<optional<T>>()(o)`
evaluates to the same value as `hash<remove_­const_­t<T>>()(*o)``; otherwise it
evaluates to an unspecified value.
The member functions are not guaranteed to be `noexcept`.
[caution
You may get compiler errors when your program provides specializations for
`std::hash<boost::optional<T>>`. If this happens, define macro
`BOOST_OPTIONAL_CONFIG_DO_NOT_SPECIALIZE_STD_HASH` to suppress the specializations
of `std::hash` in this library.
]
[endsect]