fn default_extend_tuple_i<I, H, G, F, E, D, C, B, A, EI, EH, EG, EF, EE, ED, EC, EB, EA>(
iter: impl Iterator<Item = (I, H, G, F, E, D, C, B, A)>,
i: &mut EI,
h: &mut EH,
g: &mut EG,
f: &mut EF,
e: &mut EE,
d: &mut ED,
c: &mut EC,
b: &mut EB,
a: &mut EA,
)