Re: [Boost-users] [multi_index] index based on case-insensitive strings

From: Boris (boriss_at_[hidden])
Date: 2007-02-23 08:05:59

On Fri, 23 Feb 2007 11:24:35 +0200, Joaquín Mª López Muñoz  
<joaquin_at_[hidden]> wrote:

> [...]Yep, it is correct, though possibly a little overkill; you could  
> use a simpler
> key
> extractor for the task at hand, like this:
>
> struct employee_case_insensitive_name_extractor
> {
>    typedef std::string result_type;
>
>    std::string operator()(const employee& x) const
>    {
>      return boost::algorithm::to_lower_copy(x.name);
>    }
> };

If the existing key extractors had a fourth template parameter to accept  
an unary function object I think it would be a bit easier to create  
user-defined key extractors? Imagine a (simplified) member defintion like  
this:

template<class Class,typename Type,Type Class::*PtrToMember,typename  
Functor>
struct member
{
   typedef Type result_type;

   Type& operator()(const Class& x)const
   {
     return Functor(x.*PtrToMember);
   }
};

Now I could create my multi_index_container like this:

typedef multi_index_container<
   employee,
   indexed_by<
     hashed_unique<member<employee, std::string, &employee::name,  
boost::algorithm::to_lower_copy> >
   >
> mi2;

Do I miss anything? If not please regard this as a proposal to improve  
Boost.Multi-index. :)

Boris