Why is ([System.Collections.ObjectModel.Collection[psobject]]1)[0] a string?

I've been using this conversion to pass objects to PowerShell.Invoke() like this:

PowerShell.Invoke([System.Collections.ObjectModel.Collection[psobject]]$obj)

I'm puzzled by this conversion from [int32] to [string].

Steps to reproduce

([System.Collections.ObjectModel.Collection[psobject]]1)[0].GetType().Name

Expected behavior

I expected 1 to remain an [int32].

int32

Actual behavior

1 is converted to a [string]

string

Environment data

> $PSVersionTable
Name                           Value
----                           -----
PSVersion                      6.1.0-preview.688
PSEdition                      Core
GitCommitId                    v6.1.0-preview.688
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

I have no explanation, but 2 quick additional observations:

It only happens when you cast a scalar; ([System.Collections.ObjectModel.Collection[psobject]] (, 1))[0].GetType().Name yields Int32, as expected.
It also happens with [System.Collections.Generic.List[object]]; by contrast:
- casting a scalar to [System.Collections.ArrayList] fails,
- but works correctly with [object[]]

It looks like { Write-Object $obj -NoEnumerate }.Invoke() is a more reliable way to convert to [Collection[psobject]]. Or at least is was before #2038, and (hopefully) will be again once those issues are corrected. In the meantime Write-Output2 from 6451(comment) seems to work.

If you're not concerned about the intermediate, transient [object[]] array that is invariably constructed, you can also do [System.Collections.Generic.List[object]] @($obj)

It seems that given conversion covered here:

PowerShell/src/System.Management.Automation/engine/LanguagePrimitives.cs

Line 5399 in bbb4f2e

converter = LanguagePrimitives.ConvertNumericIConvertible;

And ConvertNumericIConvertible specifically do conversion thru string:

PowerShell/src/System.Management.Automation/engine/LanguagePrimitives.cs

Lines 3858 to 3859 in bbb4f2e

    
           // If the original object was a number, then try and do a conversion on the string 
        
           // equivalent of that number...

 // If the original object was a number, then try and do a conversion on the string 
 // equivalent of that number...

Interesting. That is clearly deliberate. But why do that?

I'm not sure this really is deliberate, I think another explanation is that this is just a symptom of PowerShell being especially permissive with conversions.

Based on this check:

PowerShell/src/System.Management.Automation/engine/LanguagePrimitives.cs

Line 5395 in bbb4f2e

if (!toType.IsArray)

it feels like an oversight to have allowed the conversion to collections other than array.

I feel like this isn't purposeful and some if going on weird here. This is a PowerShell code showing the same and other weird issues.

Code

$orig_notworking = ([System.Collections.ObjectModel.Collection[psobject]]1)
echo "orig_notworking - $($orig_notworking[0].GetType().Name)"

$orig_working = (New-Object -TypeName System.Collections.ObjectModel.Collection[psobject])
$orig_working.Add([psobject]1)
echo "orig_working - $($orig_working[0].GetType().Name)"

Removed a incorrect example showing a different error. Was my fault.

#Shows that the original creation of the psobject is equivalent
echo '(New-Object -TypeName PSObject -ArgumentList @(1)) -eq [psobject]1)'
(New-Object -TypeName PSObject -ArgumentList @(1)) -eq [psobject]1

$notworking = ([System.Collections.ObjectModel.Collection[psobject]](New-Object -TypeName PSObject -ArgumentList @(1)))
echo "notworking - $($notworking[0].GetType().Name)"

$working = (New-Object -TypeName System.Collections.ObjectModel.Collection[psobject])
$working.Add((New-Object -TypeName PSObject -ArgumentList @(1)))
echo "working - $($working[0].GetType().Name)"

Output

orig_notworking - String
orig_working - Int32
#Removed output from my mistake code above from this list
(New-Object -TypeName PSObject -ArgumentList @(1)) -eq [psobject]1)
True
notworking - String
working - Int32

Sorry for the terrible code and the old post revival, but I got interested. It feels like the constructor and/or assignment operator is doing something weird.

KnowledgeNerd

KnowledgeNerd, you assign to $orig_work_but_not_working the result of calling Add, which is void, and not the collection.

Ohhh nice catch. I'll remove that one example. Still interesting that the add doesn't convert the int to string but instantiating it using the constructor with initial values does.

This issue has not had any activity in 6 months, if this is a bug please try to reproduce on the latest version of PowerShell and reopen a new issue and reference this issue if this is still a blocker for you.

Gotta say I revisited this again and was appalled at my code... But I still think something is weird.

Check out this ~slightly~ better and cleaner code to see what's going on:

$testobj = New-Object -TypeName PSObject -ArgumentList @(1)
$testobj2 = [psobject]1
$testobj3 = 1


$test = New-Object -TypeName System.Collections.ObjectModel.Collection[psobject]
$test.Add($testobj)
$test[0].gettype().name

$test2 = [System.Collections.ObjectModel.Collection[psobject]]($testobj)
$test2[0].gettype().name


$test3 = New-Object -TypeName System.Collections.ObjectModel.Collection[psobject]
$test3.Add($testobj2)
$test3[0].gettype().name

$test4 = [System.Collections.ObjectModel.Collection[psobject]]($testobj2)
$test4[0].gettype().name


$test5 = New-Object -TypeName System.Collections.ObjectModel.Collection[psobject]
$test5.Add($testobj3)
$test5[0].gettype().name

$test6 = [System.Collections.ObjectModel.Collection[psobject]]($testobj3)
$test6[0].gettype().name

Output

Int32
String

Int32
String

Int32
String

This issue has been marked as "No Activity" as there has been no activity for 6 months. It has been closed for housekeeping purposes.

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Why is ([System.Collections.ObjectModel.Collection[psobject]]1)[0] a string? #7154

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Removed a incorrect example showing a different error. Was my fault.

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	// If the original object was a number, then try and do a conversion on the string
	// equivalent of that number...

Why is ([System.Collections.ObjectModel.Collection[psobject]]1)[0] a string? #7154

Description

Steps to reproduce

Expected behavior

Actual behavior

Environment data

Activity

mklement0 commented on Jun 24, 2018

alx9r commented on Jun 24, 2018

mklement0 commented on Jun 24, 2018

PetSerAl commented on Jun 24, 2018

alx9r commented on Jun 24, 2018

lzybkr commented on Jun 25, 2018

KnowledgeNerd commented on Jun 3, 2022

Code

Removed a incorrect example showing a different error. Was my fault.

Output

PetSerAl commented on Jun 3, 2022

KnowledgeNerd commented on Jun 3, 2022

microsoft-github-policy-service commented on Nov 16, 2023

microsoft-github-policy-service commented on Nov 16, 2023

microsoft-github-policy-service commented on Nov 16, 2023

KnowledgeNerd commented on Nov 17, 2023

Output

microsoft-github-policy-service commented on Nov 25, 2023

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