reactor-core/src/main/java/reactor/util/function/Tuple4.java
public <R> Tuple4<T1, T2, R, T4> mapT3(Function<T3, R> mapper) {
		return new Tuple4<>(t1, t2, mapper.apply(t3), t4);
	}
public <R> Tuple4<T1, T2, R, T4> mapT3(Function<T3, R> mapper) {
		return new Tuple4<>(t1, t2, mapper.apply(t3), t4);
	}
Map the 3rd part (T3) of this {@link Tuple4} into a different value and type,
keeping the other parts.

@param mapper the mapping {@link Function} for the T3 part
@param <R> the new type for the T3 part
@return a new {@link Tuple4} with a different T3 value