I never like to hear the words "size of" since it is not the sizeof that a C programmer will want.

Also I am embarassed to say that I do not know or maybe have forgotten when it is that scalar @array -1 != $#array. For example an array with a single element at index 5 will give the same results for both. Or are we talking about some kind of pruning?

That said I hate evaluating arrays as a scalar anyway since I expect something bad could happen (tm). Probably the important information I promptly forgot was distilled to this inchoate fear. Say it isn't so!

Originally posted as a Categorized Answer.