This page is a snapshot from the LWG issues list, see the Library Active Issues List for more information and the meaning of CD1 status.
Section: 19.14.18 [unord.hash] Status: CD1 Submitter: Thorsten Ottosen Opened: 2008-06-05 Last modified: 2016-02-10
Priority: Not Prioritized
View other active issues in [unord.hash].
View all other issues in [unord.hash].
View all issues with CD1 status.
In the current working draft, std::hash<T> is specialized for builtin types and a few other types. Bitsets seems like one that is missing from the list, not because it cannot not be done by the user, but because it is hard or impossible to write an efficient implementation that works on 32bit/64bit chunks at a time. For example, std::bitset is too much encapsulated in this respect.
Add the following to the synopsis in 19.14 [function.objects]/2:
template<class Allocator> struct hash<std::vector<bool,Allocator>>; template<size_t N> struct hash<std::bitset<N>>;
Modify the last sentence of 19.14.18 [unord.hash]/1 to end with:
... and std::string, std::u16string, std::u32string, std::wstring, std::error_code, std::thread::id, std::bitset, and std::vector<bool>.