code: public <R> Tuple8<R, T2, T3, T4, T5, T6, T7, T8> mapT1(Function<T1, R> mapper) {
  		return new Tuple8<>(mapper.apply(t1), t2, t3, t4, t5, t6, t7, t8);
  	}
docs: Map the 1st part (T1) of this {@link Tuple8} into a different value and type,
  keeping the other parts.
  
  @param mapper the mapping {@link Function} for the T1 part
  @param <R> the new type for the T1 part
  @return a new {@link Tuple8} with a different T1 value