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From: Tobias Schwinger (tschwinger_at_[hidden])
Date: 20041011 02:25:52
Jonathan Turkanis wrote:
> "Tobias Schwinger" <tschwinger_at_[hidden]> wrote in message
> news:ckbu5h$acq$1_at_sea.gmane.org...
>
>>Alexander Nasonov wrote:
>>
>>>I have one addition to '[type_traits] "member_function_pointer_traits" ?'
>>>thread started long time ago (29 Jul 2004) by Tobias Schwinger.
>>>Is it makes sense to modify as_sequence to convert function type into a
>>>sequence? Eg:
>>>as_sequence<R (T0,T1)> > vector<R,T0,T1>
>>>as_sequence<R(*)(T0,T1)> > vector<R,T0,T1>
>>>as_sequence<R(&)(T0,T1)> > vector<R,T0,T1>
>>>
>>>as_sequence<R(C::*)(T0,T1)> > vector<R,C,T0,T1>
>>
>>as_sequence<R(T0,T1)> reads great, but this would add a lot to the
>>complexity of 'as_sequence':
>>
>>First we have to idenitify if T is some sort of function (ptr/ref) type.
>>Although there are ways to detect (not decompose, that is) functions and
>>even member function pointers without using an unrolled cascades of
>>specializations for different function arities, it requires a very
>>standard compliant compiler.
>>As we need to decompose the type and wrap its components into a vector
>>in case it turns out to be a function anyway, we will instantiate one of
>>these (more than 100) specializations.
>
>
> I don't understand why this would be hard. Here's how I would do it:
I meant what has to happen _inside_ the function_arguments metafunction.
And the fact that it has to be defined at the point of this code:
> template<typename F>
> struct as_sequence_non_member {
> typedef typename
> mpl::push_front<
> typename
> function_arguments<
> F
> >::type,
> typename
> function_result<
> F
> >::type
> >::type type;
> };
>
> template<typename F>
> struct as_sequence_member {
> typedef typename
> mpl::push_front<
> typename
> function_arguments<
> F
> >::type,
> typename
> function_class<
> F
> >::type
> >::type result;
> typedef typename
> mpl::push_front<
> result,
> typename
> function_result<
> F
> >::type
> >::type result;
> };
>
> template<typename F>
> struct as_sequence
> : mpl::if_<
> is_member_function_pointer<F>,
> as_sequence_member<F>
> as_sequence_non_member
> >::type
> { };
However, I guess you are talking about another as_sequence distinct from
mpl::as_sequence...
> Last night I realized I needed the ability to manipulate function types as
> sequences, so I wrote a small library to do it. I just finished documenting it:
>
> http://home.comcast.net/~jturkanis/function_traits/
>
> It differs from your library as follows:
>
>  it splits up the metafunction signature into several metafunctions
>  it allows function types to be constructed from sequences
>  it doesn't handle volatility.
>
> It's not really meant to compete with your proposal  I wrote it for a project
> I am currently working on. However, I'd like to know your opinion about it.
I'll have a closer look at it this evening.
Regards,
Tobias
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