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2026. hash should be std qualified for unordered container

Section: 21.5 [unord] Status: NAD Submitter: Pete Becker Opened: 2011-02-07 Last modified: 2016-02-10

Priority: Not Prioritized

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Discussion:

Tom Plum pointed out to me that there's an apparent inconsistency in the std:: qualification of template names in the unordered containers:

 template <class Key,
           class T,
           class Hash = hash<Key>,
           class Pred = std::equal_to<Key>,
           class Alloc = std::allocator<std::pair<const Key, T> > >
   class unordered_map;

Is there a reason that hash is not qualified with std::? TR1 also does not use std:: here.

[ 2011-02-07 Chris Jefferson adds: ]

I assumed (I might be wrong) it is because hash is designed to be a customisation point, like swap.

[ 2011-02-07 Howard Hinnant adds: ]

I think this is incorrect. We mean std::hash, though clients are free to specialize std::hash on user-defined types. With the possible exception of begin/end (which I'm not sure if we've settled that), swap is the only intended customization point (look up a function by ADL) in the std:: lib.

[ 2011-02-24 Chris Jefferson adds: ]

I recommend NAD, due to 15.5.1.1 [contents] p3:

Whenever a name x defined in the standard library is mentioned, the name x is assumed to be fully qualified as ::std::x, unless explicitly described otherwise. For example, if the Effects section for library function F is described as calling library function G, the function ::std::G is meant.

[2011-02-25 Reflector discussion]

Moved to Tentatively NAD after 5 votes.

Proposed resolution: