So $x = 42 is as useful as 1 = 42

I don't understand this statement. I can see where an expression like $x = 42 might be useful, but 1 = 42 can't possibly be useful because it won't compile.

Update: Or do you mean "if $x is aliased to a literal value (e.g., 1), $x = 42 is equivalent to 1 = 42"? (Update: And specifically WRT to the for-loop here? I didn't look back far enough. :)