Re: [Boost-users] [BOOST.PREPROCESSOR] Use BOOST_PP_REPEAT in macros?

Subject: Re: [Boost-users] [BOOST.PREPROCESSOR] Use BOOST_PP_REPEAT in macros?
From: Edward Diener (eldiener_at_[hidden])
Date: 2013-09-09 23:32:26

On 9/9/2013 9:06 AM, Sergey Zhuravlev wrote:
> Write code:
> //////////////////
> #define ARGS_AMOUNT 9
> #define INTERNAL_GENERATE_MEMBER_APPLY_CLASS(_, ARG_COUNTER, MemberName)\
>    template<class TClassWithMember BOOST_PP_COMMA_IF(ARG_COUNTER)
> BOOST_PP_ENUM_PARAMS(ARG_COUNTER, class TArg)>\
>    result_type operator()(\
>      TClassWithMember& classWithMember BOOST_PP_COMMA_IF(ARG_COUNTER)\
>      BOOST_PP_ENUM_BINARY_PARAMS(ARG_COUNTER, TArg, &arg)) const\
>      {\
>         classWithMember.MemberName(BOOST_PP_ENUM_PARAMS(ARG_COUNTER, arg));\
>      }
>
> #define DECLARE_MEMBER_APPLY_CLASS(TMemberApplyClassName, MemberName)\
>    template<class TResultType>\
>    struct TMemberApplyClassName\
>    {\
>       typedef TResultType result_type;\
>       BOOST_PP_REPEAT(ARGS_AMOUNT, INTERNAL_GENERATE_MEMBER_APPLY_CLASS,
> MemberName)\
>    };
> #undef ARGS_AMOUNT
> //////////////////
>
> DECLARE_MEMBER_APPLY_CLASS(TClassName, MemberName) declare class
> template closer to boost::apply, but my declared class call member
> MemberName: f.MemberName(args...); opposite f.operator()(args...) at
> boost::apply.
> Code not work correctly, because ARGS_AMOUNT not replaced to number 9
> internally. ARGS_AMOUNT preserved after all macros substitution.
> If manualy replace text "ARGS_AMOUNT" at "call" for BOOST_PP_REPEAT in
> macros DECLARE_MEMBER_APPLY_CLASS to 9, then code generated and work
> correctly.
> Why it does? How preserve valuable name of const ARGS_AMOUNT?

When you invoke DECLARE_MEMBER_APPLY_CLASS the macro ARGS_AMOUNT is not 
defined. Macros do not get expanded until you invoke them.