${ isn't an operator itself - it has to be book-ended with a }. Basically you can put any legal perl inside the {}'s - so long as it evaluates to a reference. You then de-reference according to the type. It makes for some interesting strings:

print "My scalar = ${\(my $scalar = 5)}\n";
print "My array = @{[(0..9)]}\n";
print "My array via scalar references passed to map = @{[ map {$$_} \(
+0..9) ]}\n";
print "My array returned by anonymous subroutine = @{[do {(0..9)}]}\n"
+;
print "My array formatted with join = ${\(join '*',(0..9))}\n";
print "My hash treated as array   = @{ [my %h = (0..9)] }\n";
[download]

Prints:

My scalar = 5
My array = 0 1 2 3 4 5 6 7 8 9
My array via scalar references passed to map = 0 1 2 3 4 5 6 7 8 9
My array returned by anonymous subroutine = 0 1 2 3 4 5 6 7 8 9
My array formatted with join = 0*1*2*3*4*5*6*7*8*9
My hash treated as array   = 0 1 2 3 4 5 6 7 8 9
[download]