Necessary Features

This same monk of the Elephant’s Footprint was poring over the code created by his clan. There were several competing implementations of a particular Data Access Object; at present he was attempting to decide which would become the definitive one that his clan would adopt.

“Each implementation has its own particular virtues and vexations,” said the monk to the Java master. “And each has features the others lack. I must consign all but one to the winds of oblivion. How am I to choose?”

“I cannot answer when I am thirsty,” said the master. “In the cabinet beside you are three wooden cups. Fill one from the river, the second from the temple well, and the third from the water-seller in the village. Bring all back to me without a drop spilled, and I will offer you what help I can.”

The monk did this, and set all three vessels before the master.

“What have you learned?” asked the master.

The monk bowed. “If you give a coin to the water-seller in the village, he will strike a gong twice: once before filling your cup, and again when you have had your first sip. If you fill your cup from the temple well, no gong sounds but the bucket is heavy. If you dip your cup in the river, the fish are troubled and the river-god must be appeased by a gift of ten white stones.”

“I can drink but one of these,” said the master. “Which will I find the most pleasing?”

The monk considered carefully. “The river was cold, but not altogether clear. The temple well I have drunk from in the past: its waters are bitter with limestone. And though I am not acquainted with the water-seller, I heard his gong many times today. On this evidence, I would choose the cup from the water-seller.”

“A most sensible conclusion,” said the master. “Indeed, I have visited this same water-seller every morning for eight years, and found the experience perfectly satisfying each time. Which is the vessel that he filled?”

The master sipped from the indicated cup, and his face fell in disappointment. “Young brother,” he said. “You have completely misunderstood my thirst. Where is the sound of the gong?”

The master’s thirst is unsatisfied
yet the monk has his answer—
what sound was the vessel that poured it?

The monk would have fared better
if he had set a brass censer on the window-ledge
and merely waited for rain.