Powershell: System.Collections.Queue throws error when piped to Get-Member

[Stephanevg]

Hi,

I bumped into this issue, which threw me off, at the begining since I though my Instance wasn't created.
It is impossible to list the members of our instance until we add something to the Queue.
I would expect that once I have instanciated my object, I can have a look at it's members prior to having to add something into the queue.

Steps to reproduce

$q = New-Object System.Collections.Queue
$q | gm # throws an error

$q.Enqueue("hi")
$q | gm # does not throw an error anymore, and will display the existing members.

Expected behavior

$q = New-Object System.Collections.Queue
$q | gm #should display the members that are available to us even thou the queue is still empty.

   TypeName: System.String

Name             MemberType            Definition
----             ----------            ----------
Clone            Method                System.Object Clone(), System.Object ICloneable.Clone()
CompareTo        Method                int CompareTo(System.Object value), int CompareTo(string strB), int IComparable.CompareTo(System.Obj...
Contains         Method                bool Contains(string value)
CopyTo           Method                void CopyTo(int sourceIndex, char[] destination, int destinationIndex, int count)
EndsWith         Method                bool EndsWith(string value), bool EndsWith(string value, System.StringComparison comparisonType), bo...
Equals           Method                bool Equals(System.Object obj), bool Equals(string value), bool Equals(string value, System.StringCo...
GetEnumerator    Method                System.CharEnumerator GetEnumerator(), System.Collections.IEnumerator IEnumerable.GetEnumerator(), S...
GetHashCode      Method                int GetHashCode()
GetType          Method                type GetType()
GetTypeCode      Method                System.TypeCode GetTypeCode(), System.TypeCode IConvertible.GetTypeCode()
IndexOf          Method                int IndexOf(char value), int IndexOf(char value, int startIndex), int IndexOf(char value, int startI...
IndexOfAny       Method                int IndexOfAny(char[] anyOf), int IndexOfAny(char[] anyOf, int startIndex), int IndexOfAny(char[] an...
Insert           Method                string Insert(int startIndex, string value)
IsNormalized     Method                bool IsNormalized(), bool IsNormalized(System.Text.NormalizationForm normalizationForm)
LastIndexOf      Method                int LastIndexOf(char value), int LastIndexOf(char value, int startIndex), int LastIndexOf(char value...
LastIndexOfAny   Method                int LastIndexOfAny(char[] anyOf), int LastIndexOfAny(char[] anyOf, int startIndex), int LastIndexOfA...
Normalize        Method                string Normalize(), string Normalize(System.Text.NormalizationForm normalizationForm)
PadLeft          Method                string PadLeft(int totalWidth), string PadLeft(int totalWidth, char paddingChar)
PadRight         Method                string PadRight(int totalWidth), string PadRight(int totalWidth, char paddingChar)
Remove           Method                string Remove(int startIndex, int count), string Remove(int startIndex)
Replace          Method                string Replace(char oldChar, char newChar), string Replace(string oldValue, string newValue)
Split            Method                string[] Split(Params char[] separator), string[] Split(char[] separator, int count), string[] Split...
StartsWith       Method                bool StartsWith(string value), bool StartsWith(string value, System.StringComparison comparisonType)...
Substring        Method                string Substring(int startIndex), string Substring(int startIndex, int length)
ToBoolean        Method                bool IConvertible.ToBoolean(System.IFormatProvider provider)
ToByte           Method                byte IConvertible.ToByte(System.IFormatProvider provider)
ToChar           Method                char IConvertible.ToChar(System.IFormatProvider provider)
ToCharArray      Method                char[] ToCharArray(), char[] ToCharArray(int startIndex, int length)
ToDateTime       Method                datetime IConvertible.ToDateTime(System.IFormatProvider provider)
ToDecimal        Method                decimal IConvertible.ToDecimal(System.IFormatProvider provider)
ToDouble         Method                double IConvertible.ToDouble(System.IFormatProvider provider)
ToInt16          Method                int16 IConvertible.ToInt16(System.IFormatProvider provider)
ToInt32          Method                int IConvertible.ToInt32(System.IFormatProvider provider)
ToInt64          Method                long IConvertible.ToInt64(System.IFormatProvider provider)
ToLower          Method                string ToLower(), string ToLower(cultureinfo culture)
ToLowerInvariant Method                string ToLowerInvariant()
ToSByte          Method                sbyte IConvertible.ToSByte(System.IFormatProvider provider)
ToSingle         Method                float IConvertible.ToSingle(System.IFormatProvider provider)
ToString         Method                string ToString(), string ToString(System.IFormatProvider provider), string IConvertible.ToString(Sy...
ToType           Method                System.Object IConvertible.ToType(type conversionType, System.IFormatProvider provider)
ToUInt16         Method                uint16 IConvertible.ToUInt16(System.IFormatProvider provider)
ToUInt32         Method                uint32 IConvertible.ToUInt32(System.IFormatProvider provider)
ToUInt64         Method                uint64 IConvertible.ToUInt64(System.IFormatProvider provider)
ToUpper          Method                string ToUpper(), string ToUpper(cultureinfo culture)
ToUpperInvariant Method                string ToUpperInvariant()
Trim             Method                string Trim(Params char[] trimChars), string Trim()
TrimEnd          Method                string TrimEnd(Params char[] trimChars)
TrimStart        Method                string TrimStart(Params char[] trimChars)
Chars            ParameterizedProperty char Chars(int index) {get;}
Length           Property              int Length {get;}

Actual behavior

$q = New-Object System.Collections.Queue
$q | gm # throws an error

gm : You must specify an object for the Get-Member cmdlet.
At line:1 char:6
+ $q | gm # throws an error
+      ~~
    + CategoryInfo          : CloseError: (:) [Get-Member], InvalidOperationException
    + FullyQualifiedErrorId : NoObjectInGetMember,Microsoft.PowerShell.Commands.GetMemberCommand

Environment data

> $PSVersionTable
Name                           Value
----                           -----
PSVersion                      5.1.14393.1884
PSEdition                      Desktop
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
BuildVersion                   10.0.14393.1884
CLRVersion                     4.0.30319.42000
WSManStackVersion              3.0
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1

[markekraus]

@Stephanevg Please note that this repo is only for PowerShell Core (6.0.0) issues. Windows PowerShell (5.1) issues should be filed on UserVoice.

I have reproduced this for you on

Name                           Value
----                           -----
PSVersion                      6.0.0-rc
PSEdition                      Core
GitCommitId                    v6.0.0-rc
OS                             Microsoft Windows 10.0.15063
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

This appears to be by design. System.Collections.Queue Implements IEnumerable. Enumerables are unwrapped when piped, meaning each element of the collection is sent separately through the pipeline.

Your code is equivalent to

@() | Get-Member

You can avoid this unwrapping using the unary comma operator:

,$q | Get-Member

Or using the -InputObject parameter:

Get-Member -InputObject $q