static <A> A mapMethodLike switchIfLongerInField(S field, A newOne, A oldOne) {
  ret switchIfLongerInField(field, newOne, oldOne, null);
}

static <A> A mapMethodLike switchIfLongerInField(S field, A newOne, A oldOne, Runnable onSwitch) {
  ret oldOne == null ? with(onSwitch, newOne)
    : newOne == null ? oldOne
    : cmp(l(getOpt(newOne, field)), l(getOpt(oldOne, field))) > 0 ? with(onSwitch, newOne) : oldOne;
}

Began life as a copy of #1024019