$function() and $$variable

Question

What the heck is $function(); and $$variable for?

Have never heard of these before, and searching on google doesn\'t give anything useful

Answer 1

$function() is a variable function and $$variable is a variable variable.

Those linked pages should give you plenty to go on, or at the very least some actual words to search with.

Answer 2

$$variable can be quite useful. What it does:

$a = 1;
$b = "a";
echo $$b;

Outputs 1