If a selection on multiple arguments for a type generic expression is wanted, and all types in question are arithmetic types, an easy way to avoid nested _Generic expressions is to use addition of the parameters in the controlling expression:
int max_int(int, int);
unsigned max_unsigned(unsigned, unsigned);
double max_double(double, double);
#define MAX(X, Y) _Generic((X)+(Y), \
int: max_int, \
unsigned: max_unsigned, \
default: max_double) \
((X), (Y))
Here, the controlling expression (X)+(Y) is only i