Re: [boost] [extension] factory_map::get() suggestion

From: vicente.botet (vicente.botet_at_[hidden])
Date: 2008-07-04 16:50:52

----- Original Message ----- 
From: "Robert Dailey" <rcdailey_at_[hidden]>
To: <boost_at_[hidden]>
Sent: Friday, July 04, 2008 2:49 AM
Subject: Re: [boost] [extension] factory_map::get() suggestion

>
> On Thu, Jul 3, 2008 at 7:36 PM, Jeremy Pack <rostovpack_at_[hidden]> wrote:
>> Steven,
>>
>> Yeah, it isn't quite that simple. I read the original post too quickly 
>> and
>> thought he was referring to a different function.
>>
>> I originally had a type for that std::map<int, factory<word> >, so it 
>> would
>> be something like type_factory_map<int, word>, which isn't much terser.
>> (thus, I removed it)
>>
>> I think the best solution here is to make your own typedefs for your
>> specific case.
>>
>> There are a couple of other places in the library though where I intend 
>> to
>> add the type of typedefs suggested.
>>
>> Jeremy
>>
>> On Thu, Jul 3, 2008 at 5:26 PM, Steven Watanabe <watanabesj_at_[hidden]>
>> wrote:
>>
>>> AMDG
>>>
>>> Jeremy Pack wrote:
>>>
>>>> Yep! Good idea. I'll take care of it.
>>>>
>>>>
>>>>> For example, right now I have to do this:
>>>>>
>>>>> factory_map fm;
>>>>> std::map<int, factory<word> > & factory_list = fm.get<word, int>();
>>>>>
>>>>> It would be ideal to do this instead:
>>>>>
>>>>> factory_map fm;
>>>>> factory_map::type& factory_list = fm.get<word, int>();
>>>>>
>>>>>
>>>>
>>> Is it really that easy?  Doesn't the result of get
>>> depend on the particular template arguments?
>>> I don't quite see how you can get away with a
>>> single typedef.
>>>
>>> In Christ,
>>> Steven Watanabe
>>>
>>>
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>
> Why not turn factory_map::get() into a template utility class of some
> sort instead of a function? That would give you the ability to typedef
> the std::map. Perhaps another option is to do the following:
>
> factory_map<word, int>::get()
>
> I don't have time right now to give any reasonable ideas, but those
> are just some thoughts off the top of my head. Later on I may try to
> help find an alternative to this. All I know for sure is that exposing
> std::map seems like an implementation detail, and specifying the same
> template parameters more than once also bothers me slightly.
> _______________________________________________
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>

Hello,

Maybe you are thinking on something like:

struct factory_map {
    template <typename A, typename B>
    struct getter {
        typedef std::map<A, factory<B> > type;
        static type& apply(factory_map&fm){return fm.get<A,B>();}
    };
};
factory_map fm;
typedef factory_map::getter<word, int> factory_map_getter;
factory_map_getter::type& factory_list = factory_map_getter::apply(fm);

Vicente