How can I get an empty list instead of null?

Question

Suppose I have a couple of arrays:

$a = 1,2,3
$b = 4,5,6

and I get the intersection (empty):

$c = $a |?{$b -contains $_}

I would expect $c to contain an empty list such that I could do:

$c.length

but I don't. I get a $null (which issues an exception when queried for .length). How can I get an empty list back instead?

Answer 1

Wrap it in the array constructor:

$c = @($a | ? { $b -contains $_ })