My point is that the real issue is just whether or not the function call is compiled as part of the same unit as the function. If it is, then, certainly, modern

My point is that the real issue is just whether or not the function call is compiled as part of the same unit as the function. If it is, then, certainly, modern C compilers can inline functions called via function pointers. The inlining itself is not made easier via the template magic. Your C comparator function is already “monomirphized” - it’s just not type safe.