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### 2817. `std::hash` for `nullptr_t`

Section: 22.10.19 [unord.hash] Status: Resolved Submitter: Marshall Clow Opened: 2016-11-10 Last modified: 2020-09-06

Priority: Not Prioritized

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Discussion:

In the list of types that the library provides `std::hash` specializations, there is an entry for `hash<T*>`, but none entry for `hash<nullptr_t>`.

[2016-11-13, Daniel provides wording]

[2016-11-28]

Resolved by P0513R0

Proposed resolution:

This wording is relative to N4606.

1. Change 22.10 [function.objects], header `<functional>` synopsis, as indicated:

   >     […]

   >     // Hash function specializations
   >     template <> struct hash<bool>;
   >     […]
   >     template <> struct hash<long double>;
   >     template <> struct hash<nullptr_t>;

   >     template<class T> struct hash<T*>;
   >     […]

2. Change 22.10.19 [unord.hash] before p2, as indicated:

   >     template <> struct hash<bool>;
   >     […]
   >     template <> struct hash<long double>;
   >     template <> struct hash<nullptr_t>;
   >     template<class T> struct hash<T*>;