Question

My source code:

# $arr = @(); results in same behaviour
$arr = New-Object System.Collections.ArrayList;

$arr.Count;
$arr += "z";

$arr.Count;
$arr.Clear();
$arr.Count;

Output:

0
1
1

Answer 1

Powershell does some array-casting trickery when you do +=, so the easy solution is to do $arr.Add("z"). Then $arr.Clear() will act like you expect.

To clarify:

1. @() is a Powershell array. It uses +=, but you can’t Clear it. (You can, however, do $arr = @() again to reset it to an empty array.)
2. ArrayList is the .NET collection. It uses .Add, and you can Clear it, but for some reason if you += it, Powershell does some weird array coercion. (If any experts care to comment on this, awesome.)