Add-Member enhancements in PowerShell 3.0

PowerShell 3.0 offers new ways to add Note properties to objects. In PowerShell 2.0, a typical command to do that would look like:

PS> New-Object -TypeName PSObject | 
Add-Member -MemberType NoteProperty -Name One -Value 1 -PassThru

One
---
  1

And when adding multiple note properties:

PS> New-Object -TypeName PSObject | 
      Add-Member -MemberType NoteProperty -Name One -Value 1 -PassThru | 
      Add-Member -MemberType NoteProperty -Name Two -Value 2 -PassThru | 
      Add-Member -MemberType NoteProperty -Name Three -Value 3 -PassThru


One Two Three
--- --- -----
  1   2     3

As you can see the syntax was very long and each time you created a NoteProperty you had to specify that. In Powershell 3.0 Add-Member have to new parameters: NotePropertyName and NotePropertyValue. Now you can easily add a NoteProperty without having to specify the member type and without having to specify parameter names, we take advantage of their positional value.

PS> New-Object -TypeName PSObject | Add-Member One 1

One
---
  1

To add multiple NoteProperty we can now use a hashtable:

PS> New-Object -TypeName PSObject | Add-Member @{One=1; Two=2; Three=3} -PassThru

One Three Two
--- ----- ---
  1     3   2

Notice that the object we got back didn't preserve the order of properties defined in the hashtable. Order in a dictionary is defined the moment you create it and the regular hashtable syntax @{} is an unordered dictionary. To make sure properties are listed in the order we defined them, we use an ordered hashtable.

PS> $pso = New-Object -TypeName PSObject
PS> $pso | Add-Member ([ordered]@{One=1; Two=2; Three=3}) -PassThru

One Two Three
--- --- -----
  1   2     3

Finally, there's another interesting new parameter: TypeName. We can use it to specify a name for the resultant object type. This is very useful when you use format files to define the default display of your objects. Previously we had to add the type name to the object's PSTypeNames list, now it is even easier.

PS> $pso = New-Object -TypeName PSObject 
PS> $pso | Add-Member ([ordered]@{One=1; Two=2; Three=3}) -TypeName MyType.MyObject 
PS> $pso | Get-Member

   TypeName: MyType.MyObject

Name        MemberType   Definition                    
----        ----------   ----------                    
Equals      Method       bool Equals(System.Object obj)
GetHashCode Method       int GetHashCode()             
GetType     Method       type GetType()                
ToString    Method       string ToString()             
One         NoteProperty System.Int32 One=1            
Three       NoteProperty System.Int32 Three=3          
Two         NoteProperty System.Int32 Two=2