Given that this works:
$ar = @()
$ar -is [Array]
True
Why doesn't this work?
function test {
$arr = @()
return $arr
}
$ar = test
$ar -is [Array]
False
That is, why isn't an empty array returned from the test function?
Your function doesn't work because PowerShell returns all non-captured stream output, not just the argument of the return statement. An empty array is mangled into $null in the process. However, you can preserve an array on return by prepending it with the array construction operator (,):
function test {
$arr = @()
return ,$arr
}
answered Aug 27 '13 at 23:19
-
1soooooo frustrating. If you return @(/*some filtered expression that has zero elements*/) you also encounter the same behaviour. return ,@(/*expr*/) is a fix... but it's hacky as hell. So easy to overlook. – Steven Evers Mar 28 '14 at 23:18
-
This stupid workings cost me about a day in freaking time. I could not figure out how my script was double the values in the array. Thank you for posting that. Why would they even think that was a good idea for functions! So frustrating! The worst part is, I had an
$arr.add(1)which was outputting the count of the array after. Doing$x = $arr.add(1)fixed the issue. Hacky. – Jim W. Jul 3 '14 at 15:14 -
@BradFJacobs: You could also use
... | Out-Nullor... >$nullto suppress undesired output. I wouldn't consider returning all non-captured output a bad idea per se, though, it's just unexpected for most people with a background in other programming languages. When used properly it can actually simplify returning data from a function, because you don't have to collect all desired output in a variable before returning it. – Ansgar Wiechers Jul 5 '14 at 20:50 -
2@BradFJacobs, while this is normally true, I think return was just a mistake. According to Bruce Payette (one of PowerShell's designers) the return statement was added for control flow, and
return $xis just shorthand forWrite-Output $x; return. Clearly the keyword should be ExitSub and it shouldn't accept an argument. – Sam Porch May 20 '15 at 1:21 -
1Actually it behaves differently if returned from a function vs locally, locally it does create an array of size 1 containing an empty array, but when returned from a function PS seems to be unwrapping the outer layer and giving an empty array – illegal-immigrant Jun 22 '17 at 18:57
write-output $arr is as afaik the same as just writing $arr.
So the function will still return $null.
But write-output has the option -NoEnumerate.
That means the empty Array will not be enumerated
(and therefore ignored - because it's empty). The result is an empty array.
admittedly the above answer is much shorter, ...
function test {
$arr = @()
write-output $arr -NoEnumerate
}
(test) -is [array] ## $True
