- Oracle (as CONVERT([val] DEFAULT [expr] ON CONVERSION ERROR)
I would love to implement it myself, but my knowledge of C is superficial.
It's is interesting feature - and implementation can be very easy - but without enhancing type API this function can be pretty slow.
So there is a dilemma - simple implementation (few work) but possible very negative performance impact under higher load due work with savepoints, or much larger work (probably easy) without necessity to use safepoints.