Steven,

thanks a lot for your answers. That could help, but I would like to have some simple interface for the user. I don't want users write a lot of template classes where they would not really understand the background.


In the current approach X4 is the trait type:

Asking the users to write:

(X1)(X2)(X3)((traitX<T1)(T2>)) is not a great idea.


As well as:
(X1)(X2)(X3)(paranthesized_type(wrap<traitX<T1, T2> >))


I could try doing it in the background and still ask users write:

(X1)(X2)(X3)((traitX<T1,T2>))

I just thought there could be a simpler way of doing it.


Many thanks for your help,

Ovanes





On Jan 28, 2008 7:12 PM, Steven Watanabe <watanabesj@gmail.com> wrote:
AMDG

Ovanes Markarian wrote:
> Hello *,
>
>
> I have some pre-processor sequence in form of:
>
> (X1) (X2) (X3) (X4)
>
> which is expanded by BOOST_PP_SEQ_FOR_EACH to template parameters:
>
> some_template<X1, X2, X3, X4> ...
>
>
> My problem now is that some of Xn parameters can be a template
> instantiation and that actually causes PP to think, that there are
> more parameters to the function applied by ..._SEQ_FOR_EACH.
> Example: some_other_template<T1, T2> cause preprocessor to think that
> there are 2 params some_other_template<T1 and T2>.
>
> Putting the parameter into additional braces like ((X4)) results in
> the template:
>
> some_template<X1, X2, X3, (X4)> and that results in a compiler error.
> I know this construct can switch off ADL, but I don't know why it
> result here in a compiler error, since I fully qualify the X4 (from
> which namespace it is). Is there any way to treat Xn as a single
> paramer but during the final pre-processing stage get rid of
> additional braces?
>

There are a couple of ways to do it.  You can make each element of the
Seq to be itself a seq
and then call BOOST_PP_SEQ_ENUM on the inside:

((X1))  ((X2))  ((some_other_template<T1)(T2>))

Another way is to use template metaprogramming

(X1)(X2)(parenthesize_type(wrap<some_other_template<T1, T2>>))

template<class T>
struct unparenthesize { typedef T type; };

template<class T>
struct unparenthesize<parenthesized_type(wrap<T>)> { typedef T type; };

In Christ,
Steven Watanabe

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