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In what conditions does operator [] return AutomationNull? #6436
Description
Chapter 7.1.4 of the PowerShell spec indicates that for arrays, strings, hashtables, and XML documents operator [] returns $null for non-existent indexes. The spec seems to be silent for other types, however. I expected that, for other types, operator [] would also return $null for non-existent indexes. It seems that for some combinations of types and indexes, however, operator [] returns AutomationNull. In what conditions does operator [] return AutomationNull?
Steps to reproduce
&{(1)[1]} | % {'output from indexing [int] out-of bounds'}
&{(,1)[1]} | % {'output from indexing array out-of-bounds'}Expected behavior
output from indexing [int] out-of bounds
output from indexing array out-of-bounds
Actual behavior
output from indexing array out-of-bounds
Environment data
> $PSVersionTable
Name Value
---- -----
PSVersion 6.0.0
PSEdition Core
GitCommitId v6.0.0
OS Microsoft Windows 6.3.9600
Platform Win32NT
PSCompatibleVersions {1.0, 2.0, 3.0, 4.0...}
PSRemotingProtocolVersion 2.3
SerializationVersion 1.1.0.1
WSManStackVersion 3.0
Activity
alx9r commentedon Mar 20, 2018
I think the logic is here, but I only have a guess at what that code does.
alx9r commentedon Mar 21, 2018
It looks like this is different behavior from selecting a non-existent property. Selecting a non-existent property seems to always output
$nullnotAutomationNull:outputs
mklement0 commentedon Mar 22, 2018
Indeed, accessing a nonexistent property always returns
$null, whether applied to a scalar or a collection.By contrast, indeed,
[System.Management.Automation.Internal.AutomationNull]::Value,$nullwhich is an interesting inconsistency (for which I have no explanation).