Re: [Boost-users] [pre-processor ] help needed

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)) is not a great idea. As well as: (X1)(X2)(X3)(paranthesized_type(wrap >)) I could try doing it in the background and still ask users write: (X1)(X2)(X3)((traitX)) 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 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 ...

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 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 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))

Another way is to use template metaprogramming

(X1)(X2)(parenthesize_type(wrap>))

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

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

In Christ, Steven Watanabe

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