i have used the MissingThing approach a few times, incl. as specific pre-existing NullRecord in SQL db to avoid having null-FKs. But also as NotPassed singleton

i have used the MissingThing approach a few times, incl. as specific pre-existing NullRecord in SQL db to avoid having null-FKs. But also as NotPassed singleton for default func args etc. In Some cases it worked perfect (like in math: 0 is just another number - as long as you don't divide by it), sometimes it needed extra "arithmetic", but still worked... and Sometimes it did not work.. and was abandoned, as handling nulls was much easier than handling ThisSpecial stuff. Sometimes it is possible to avoid the zero thing all-together but needs a magnitude more thinking on higher levels of abstraction. btw: has anyone heard of array-of-negative-size? Like a eating hole (if positives are a peg) .. 5 + -3 == 2, so app-ending such 3-hole to a 5-peg array will shorten it to first 2 only..