For cases where one has already assigned DownValues associated with the name 'a', is there an accepted way to block the assignment of OwnValues to the same name? (I originally came across this issue while playing with someone's attempt at implementing a data dictionary.)
Here's what I mean to avoid:
Remove[a];
a[1] := somethingDelayed
a[2] = somethingImmediate;
DownValues[a]
a[1]
a[2]
Returns...
{HoldPattern[a[1]] :> somethingDelayed,
HoldPattern[a[2]] :> somethingImmediate}
somethingDelayed
somethingImmediate
And now if we were to evaluate:
a = somethingThatScrewsUpHeads;
(* OwnValues[a] above stored in OwnValues *)
a[1]
a[2]
We get...
somethingThatScrewsUpHeads[1]
somethingThatScrewsUpHeads[2]
Is there an easy/flexible way to prevent OwnValues for any Name in DownValues? (Lemme guess... it's possible, but there's going to be a performance hit?)