[boost] [multi_index] feature proposal: member keys and typeless specification of keys

Subject: [boost] [multi_index] feature proposal: member keys and typeless specification of keys
From: JOAQUIN M. LOPEZ MUÑOZ (joaquin_at_[hidden])
Date: 2011-05-08 07:31:32

Hi all,

This is a proposal for inclusion of two new features into Boost.MultiIndex,
mem_key and BOOST_MULTI_INDEX_AUTO_KEY.

Consider the following:

  struct foo

  {

    int x;

    int bar();

    int baz()const;

  };

  typedef multi_index_container<

    foo,

    indexed_by<

      ordered_unique<member<foo,int,&foo::x> >,

      ordered_unique<mem_fun<foo,int,&foo::bar> >,

      ordered_unique<const_mem_fun<foo,int,&foo::baz> >

    >

  > multi_t;

Note that we have to use member, mem_fun or const_mem_fun

depending on the kind of key used. mem_key allows for a uniform

specification syntax:

  typedef multi_index_container<

    foo,

    indexed_by<

      ordered_unique<mem_key<int foo::*,&foo::x> >,

      ordered_unique<mem_key<int (foo::*)(),&foo::bar> >,

      ordered_unique<mem_key<int (foo::*)()const,&foo::baz> >

    >

  > multi_t;

This in itself gains us relatively little; but if we have a C++11 compiler

with decltype, BOOST_MULTI_INDEX_AUTO_KEY can use mem_key

in a way that dispenses with the need for specifying the type of

the key!

  typedef multi_index_container<

    foo,

    indexed_by<

      ordered_unique<BOOST_MULTI_INDEX_AUTO_KEY(&foo::x)>,

      ordered_unique<BOOST_MULTI_INDEX_AUTO_KEY(&foo::bar)>,

      ordered_unique<BOOST_MULTI_INDEX_AUTO_KEY(&foo::baz)>

    >

  > multi_t;

Some requests and questions:

1. If you're interested in these features, please download the attached

mem_key.hpp file, play with it and report on successful/problematic

usage.

2. Do you think this is worth including in Boost.MultiIndex?

3. Proposals on the naming scheme?

Thank you,

Joaquín M López Muñoz

Telefónica, Investigación y Desarrollo

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