类似于函数的宏的问题

Question

I'm trying to shorten some repetitive code in my bison parser, here's an excerpt of one of the rules:

expression : OBJECTID ASSIGN expression { $$ = std::make_shared<Assign>($1, $3); $$->setloc(@3.first_line, curr_filename); }
            | expression '.' OBJECTID '(' method_expr_list ')' { $$ = std::make_shared<DynamicDispatch>($1, $3, $5); 
                                                                 $$->setloc(@1.first_line, curr_filename); }

I was thinking of something along the lines of:

expression : OBJECTID ASSIGN expression { $$ = std::make_shared<Assign>($1, $3); SETLOC(@1); }
            | expression '.' OBJECTID '(' method_expr_list ')' { $$ = std::make_shared<DynamicDispatch>($1, $3, $5); 
                                                                 SETLOC(@1); }

I can't think of any other way to achieve this other than to use a macro to do it. This is what I came up with:

#define SETLOC(node) $$->setloc((node).first_line, curr_filename)

Unfortunately, I get a compile error saying that $$ is not defined, which makes sense since it's a function-like macro. I would like to know if there's a way to achieve the code in the 2nd snippet?

Answer 1

This is because $$ is a special sequence that Bison recognizes and uses, it's not in the actual generated C code. You have to pass it in as an argument to the macro instead:

#define SETLOC(parent, node) parent->setloc((node).first_line, curr_filename)