Powershell Script fails after accessing Array.Length Property

Question

Can someone explain why this script throws an exception?

$byteArray = @(1,2,3)
write-Output ( "{0:X}{1:X}{2:X}" -f $byteArray )
write-Output ( $byteArray.Length -ge 3 )
write-Output ( "{0:X}{1:X}{2:X}" -f $byteArray )

Basically, I am creating an array of numbers, formatting the array and then checking its length and formatting it again.

The first format succeeds, but the second format throws an exception.

123
True
--------------------------------------------------------------------------------
POWERSHELL EXCEPTION 
EXCEPTION TYPE:System.Management.Automation.RuntimeException
MESSAGE:Error formatting a string: Index (zero based) must be greater than or equal to zero and less than the size of the argument list..
POSITION:
At line:4 char:36
+ write-Output ( "{0:X}{1:X}{2:X}" -f  <<<< $byteArray )
--------------------------------------------------------------------------------

Answer 1

To add to the puzzle:

PS > $a = @(1,2,3)
PS > $b = $a
PS > [object]::ReferenceEquals($a, $b)
True
PS > $a.Length
3
PS > [object]::ReferenceEquals($a, $b)
True
PS > "{0:X}{1:X}{2:X}" -f $a
Error formatting a string: Index (zero based) must be greater than or equal to zero and less than the size of the argum
ent list..
At line:1 char:21
+ "{0:X}{1:X}{2:X}" -f  <<<< $a
PS > "{0:X}{1:X}{2:X}" -f $b
123
PS > $b.GetLength(0)
3
PS > "{0:X}{1:X}{2:X}" -f $b
123
PS > [object]::ReferenceEquals($a, $b)
True

I tend to agree with Jared that it's a quirk of the -f operator seeing the variable as an object rather than an array, supported in part by this:

PS > $a = @(1,2,3)
PS > "{0:X}{1:X}{2:X}" -f $a
123
PS > "{0:X}{1:X}{2:X}" -f $a.PSObject
Error formatting a string: Index (zero based) must be greater than or equal to zero and less than the size of the argum
ent list..
At line:1 char:21

If the underlying object isn't acceptable as a parameter, then there must be something special about how $a is originally stored that makes -f happy. But that still doesn't explain why calling GetLength() doesn't affect $b's "arrayness" in the way that Length (and Rank) seem to.

As others have noted, using @() does seem to work consistently.

Answer 2

That's definitely weird. As a workaround you can use

"{0:X}{1:X}{2:X}" -f @($byteArray)

which seems to work even after accessing members of $byteArray.

Another possible workaround might be to save the formatted string to a variable and re-use it.

As for why it doesn't work after accessing the Length property I have no idea.