1) @foo  = 
    the result of dereferencing $_[0]

2) @bar = 
    the result of dereferencing $_[0]
        if $_[0] is true
    otherwise the result of dereferencing the empty array "()"

3) @jazz = 
    the number of elements of the result of dereferencing $_[0]
        if that number is true (greater than 0)
    otherwise the empty array "()"