Fix _Hashtable extension

[François Dumont]

On 21/03/2014 23:59, Jonathan Wakely wrote:
> On 21/03/14 22:39 +0100, François Dumont wrote:
>> Hi
>>
>>    Here is a patch to fix _Hashtable Standard extension type which is 
>> almost unusable at the moment if instantiated with anything else that 
>> the types used for the std unordered containers that is to say 
>> __detail::_Default_ranged_hash and __detail::_Mod_range_hashing.
>
> Good catch.
>
> Also, it seems that this specialization is missing the "hasher"
> typedef:
>
>   /// Specialization: ranged hash function, no caching hash codes.  H1
>   /// and H2 are provided but ignored.  We define a dummy hash code type.
>   template<typename _Key, typename _Value, typename _ExtractKey,
>      typename _H1, typename _H2, typename _Hash>
>     struct _Hash_code_base<_Key, _Value, _ExtractKey, _H1, _H2, _Hash, 
> false>
>     : private _Hashtable_ebo_helper<0, _ExtractKey>,
>       private _Hashtable_ebo_helper<1, _Hash>
>     {
>
> From the comments I think it is intentional, is that right?

It seems intentional to me too even if I haven't written this code. In 
this case the user is supposed to provide a functor that gives the 
bucket index directly from the key so no real hasher even if there might 
be one in this functor.

Patch committed.

François