What value should be given to a Tcl dict for minimum memory?

Question

I need a dictionary, "just for the keys", that is, the values are of lesser importance. Which value will consume the least amount of memory? "0" "", something else? Thanks.

Answer 1

Tcl shares constants under the covers, so you can use pretty much anything as long as it is a literal. But the empty string is almost certainly going to be a pre-defined constant in your script anyway (even if you don't notice it) and is pretty short. Or go with a single-character alphanumeric string, which will generate a shorter string form of dictionary (and have practically no difference otherwise). A 0 is a single-character alphanumeric string, of course.

In my own code, I would mostly use something like "dummy value" for the value. The cost is only a few bytes total more most of the time, and yet it's much clearer to me that it doesn't mean anything, so if I come back to the code later I don't try to figure out what I was doing with the value…