Why is $args array empty when this function is called? - arrays

Question

I found an error in how the following code works, excerpted from MSFT_Archive.psm1, the Archive DSC resource.
Function Get-CacheEntry
{
$key = [string]::Join($args).GetHashCode().ToString()
Trace-Message "Using ($key) to retrieve hash value"
$path = Join-Path $CacheLocation $key
if(-not (Test-Path $path))
{
Trace-Message "No cache value found"
return #{}
}
else
{
$tmp = Import-CliXml $path
Trace-Message "Cache value found, returning $tmp"
return $tmp
}
}
The line "$key = [string]::Join($args).GetHashCode().ToString()" does the wrong thing because $args always comes out as being an empty array. A typical call to this method is:
$cacheObj = Get-CacheEntry $Path $Destination
I added print statements and $Path and $Destination have values; they are not empty or nil. Because the $args array is empty, the value of $key is always the same, and consequently all cache files get the same name, regardless of the Zip archive being unpacked. Different inputs then lead to the same cache file being consulted, leading to the same file being repeatedly unpacked even when nothing changes.
The method has no named parameters, so $args should always have the list of unbound parameters. What is wrong?
I am using Powershell 4.0 on a Windows Server 2008R2 system with DSC Resource Kit Wave 10.
UPDATE: This problem is present in both Archive and xArchive resources.

Answer 1

A function with only [string]::Join($args) will produce empty results as you have seen. As EBGreen explains you need to have at least 2 arguments in the method (depending which overload you use). As an alternative you can try to use the -join operator instead.
$key = (-join $args).GetHashCode().ToString()

Answer 2

[string]::Join() does not have a single argument overload. Try this:
$key = [string]::Join('', $args).GetHashCode().ToString()