Re: [Boost-users] [Unordered] [Multi-Index] Set lookup from something else than key_type

Subject: Re: [Boost-users] [Unordered] [Multi-Index] Set lookup from something else than key_type
From: joaquin_at_[hidden]
Date: 2009-09-02 07:41:52

Daniel James escribió:
> 2009/9/2  <joaquin_at_[hidden]>:
>   
>> Daniel James escribió:
>>     
>
>   
>>> But those overloads don't always exist. A simple example is:
>>>
>>>    struct hash {
>>>        std::size_t operator()(std::string const&) const;
>>>    };
>>>
>>>    struct equals {
>>>        bool operator()(std::string const&, std::string const&) const;
>>>    };
>>>
>>>    boost::unordered_map<std::string, int, hash, equals> map;
>>>    // ....
>>>    map.find("char array");
>>>
>>> A single string object should be created in this case.
>>>
>>>       
>> Correct, but it's the user's responsibility, not yours, to make sure the
>> hash and
>> equality functors used have the appropriate overloads.
>>     
>
> I disagree, I'd see what I wrote as reasonable use of the STL.
>   

Yep, I now see your POV and this is admittedly something people can 
disagree on.
Another possibility is that Boost.Unordered provide

  const_iterator find(const key_type& k) const;

  template<
    typename CompatibleKey,typename CompatibleHash,typename CompatiblePred
  >
  iterator find(
    const CompatibleKey& k,
    const CompatibleHash& hash,const CompatiblePred& eq)const;

which is a pure extension without backwards compatibility problems. This
is seemingly what Boost.Intrusive is doing.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo