afaik, there is not.

As an aside, I completely disagree with your statement. When I'm reading code (mine or someone elses), it is inherently easier to know the intention of $x[0] directly than it is to have to scroll through to find out first where $a came from, and then have to do it again to find out how it got back into @x (imho).

Also, using $a and $b is not advised much of the time, as they are special variables when one is using sort. This recommendation is contentious with some people, especially if you meant it only as an example... but I thought I'd point it out anyways.

Update: unless I'm misunderstanding the question, the OP does not want to use the syntax of $x[0] at all, and instead just use a single variable that references the element. I'll let OP clarify.