reactor-core/src/main/java/reactor/util/function/Tuple5.java
public <R> Tuple5<R, T2, T3, T4, T5> mapT1(Function<T1, R> mapper) {
		return new Tuple5<>(mapper.apply(t1), t2, t3, t4, t5);
	}
public <R> Tuple5<R, T2, T3, T4, T5> mapT1(Function<T1, R> mapper) {
		return new Tuple5<>(mapper.apply(t1), t2, t3, t4, t5);
	}
Map the 1st part (T1) of this {@link Tuple5} 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 Tuple5} with a different T1 value