...если комитет примет предложение представленное в этом пропозале.
Предлагается добавить «нативные» C++-макросы.
Из пропозала
So what would one of these native C++ macro functions look like?
// Macro functions look just like a free function except for the # at the // end of the function name. Note that the # counts as part of the identifier, // so return# does not collide with the return keyword. template<class T> inline int return#(T v) { if(v > 0) return -> v; // control flow keyword + ’->’ means it affects the // calling function, not this macro function if(v < 0) break ->; // Also this break is executed in the calling function // If break isn’t valid at the point of use // in the calling function, it will not compile // We can inject variable declarations into the calling function // with typename + ’->’. This is useful for RAII triggered cleanup // i.e. these get destructed when the scope of the call point exits. // Note that the actual name of the variable injected will // be some very unique identifier which cannot collide with any // other variable, including those injected by other macro functions int -> a = 5; // Otherwise this function macro has a local scope, and code // executed here remains here size_t n = 0; for(; n < 5; n++) { // We can also refer to variables previously injected into the // caller’s scope by this macro function like this. // This lets one keep state across invocations of the macro function (-> a) ++; } // This returns a value from this function macro to the caller // If you wrote return -> a, that would be a compile error // as there is no variable called a in this scope. return (-> a); }
Такие макросы могут быть полезны для реализации некоторых фич, требующих вставки кучи служебного кода, например, корутин или оператора try, без внесения модификаций в Core Language, чисто на уровне библиотек.
Также макросы могут пригодиться для замены обычных макросов, которые станут недоступны после перехода на модули.
