De: Lorenzo Caminiti <lorcaminiti@gmail.com> Objet: [boost] [mpl] is_macro_called À: boost@lists.boost.org Date: Samedi 3 avril 2010, 13h25 Hello all:
Is there a way I can check at compile-time and class-scope if a macro has been called and expanded (at least one time) from within a member function?
For example:
#define X(...) ... // Some macro definition -- the macro parameters could be anything needed to implement is_macro_called.
struct is_macro_X_called { ... }; // Some implementation -- this could be a template or something else.
So that:
struct z { void f() { X(...); // Macro called from within a member function. }
// Detect at class-scope and a compile-time that the macro was called. static const bool is_macro_X_called::value; // Evaluates to true. };
Instead:
struct z { void f() { // X(...); // Macro not called. }
static const bool is_macro_X_called::value; // Evaluates to false. };
I do not know how to program this. However, could for example the macro X() instantiate a template with some special template parameter that can then be inspected at compile-time by a is_macro_called metafunction?
Thank you very much. Lorenzo
Hello, I don't know how to do that compile time without macros. I wonder if it is possible with mpl. Anyway, maybe the following is enough for your need? [code] #include <iostream> #include <boost/preprocessor/slot/counter.hpp> #include <boost/type_traits/is_same.hpp> #define MACRO_Example(X) \ std::cout<<X<<std::endl; struct X { // at the beginning of the class. template <int Y> class MacroWasUsedHelper{}; typedef MacroWasUsedHelper<BOOST_PP_COUNTER> Before; void writeMe() { // if you comment the 2 next lines, the counter will be 0. MACRO_Example("Me"); #include BOOST_PP_UPDATE_COUNTER() } // at the end of the class declaration typedef MacroWasUsedHelper<BOOST_PP_COUNTER> After; // now you just have to compare the 2 types "Before" and "After" as you wish. the following will be 'boost::true_type' only if it was not used. typedef boost::is_same<Before, After>::type undetected; }; [/code] The elements like "typedef MacroWasUsedHelper<BOOST_PP_COUNTER> After;" can be put into a macro easily. Only the "#include BOOST_PP_UPDATE_COUNTER()" seems necessary to remain (as long as we use pure C++). Here you got compile time evaluation. It was also possible to use directly functions returning constant (BOOST_PP_COUNTER) instead of template programming. Hope this helps, Best Regards, Pierre Morcello