#include <stdio.h>
 
#define fst(x, y)              \
    ((struct {                 \
        __typeof__(x) first;   \
        __typeof__(y) second;  \
    }) {                       \
        .first = (x),          \
        .second = (y)          \
    }.first)
 
#define swap(x, y)         \
    ((void)((x) = fst((y), \
                      (y) = (x))))
 
int main(void) {
	char *x = "first", *y = "second";
	swap(x, y);
	printf("%s %s\n", x, y);
	return 0;
}
 

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