The Codeless Code: Case 135 Ass-Backwards Compatibility 
======

 Wangohan, a monk of the Spider Clan, stumbled upon a bug in
a utility class provided by the Laughing Monkey Clan. He
called upon the junior monk who was its author.

“Your last refactoring of isHexNumber was incorrect,” said
Wangohan. “Although there is no documentation, the name
implies that it will only match strings of one or more hex
digits. Yet your regular expression uses no anchors and the
wrong quantifer.  You will return true for any string in
which zero or more hex digits are present anywhere—which is
to say, any string at all.”

“I ensured that the existing unit tests passed,” protested
the junior monk. “Null is rejected, and legitimate hex
numbers are accepted.”

Wangohan scowled. “I tell you that a cardboard box is not a
fit meal for the Emperor’s daughter, and you reply, a goat
did not choke on it.”

Wangohan called on the senior monk who tended the shared
library and explained the problem.

“We cannot change the implementation,” said the senior monk.
“This method is now used throughout the Temple. If it
suddenly rejects strings it once accepted, disaster might
ensue.”

Wangohan pounded his fist on the monk’s desk. “I tell you
that a cardboard box is not a fit meal for the Emperor’s
daughter, and you reply, she may dislike the taste of lamb
and figs.”

Wangohan called upon the head abbot of Laughing Monkey and
explained the problem.

“I will attend to the matter,” sighed the abbot. “There must
be a solution which will satisfy all parties.”

That evening Wangohan received an email from the abbot,
stating that the method should now perform exactly as
expected. Wangohan brought up the code and found it to be
completely unchanged, save for a new comment at the top:

/** * isHexNumber returns true for any string * in which
zero or more hex digits are present * anywhere. */

Wangohan’s head fell to his desk. “Clearly a cardboard box
must be a fit meal for the Emperor’s daughter, for here it
is on the Imperial menu.”