.NET Type Extension

SHORT DESCRIPTION

Extending the .NET type system in the Windows PowerShell

LONG DESCRIPTION

The types.ps1xml file in the PowerShell home directory provides a mechanism for extending the .NET type system. By default, PowerShell adds a number of elements to the file to extend the .NET types. In addition, you can add other elements for your own customizations.

One way that a type can be extended is by adding a property. To add a property (or to extend a type in any way), you must modify the <type> element for the specific type in the types.ps1xml file. For example, the array type, by default, does not include a Count property, so PowerShell defines an alias property called Count. The property includes a reference member name for the Length property, as shown in the

following XML:

<Type>

<Name>System.Array</Name>

<Name>Count</Name>

Length

</ReferencedMemberName>

</AliasProperty>

</Members>

</Type>

You can verify the custom AliasProperty by using a Get-Member command to retrieve the properties of an object array, as shown in the following command:

Get-Member -inputobject (1,2,3,4) -member *property*

The command returns the following results:

TypeName: System.Object[]

Name MemberType Definition

Count AliasProperty Count = Length

IsFixed SizeProperty System.Boolean IsFixedSize {ge

IsReadOnly Property System.Boolean IsReadOnly {get

IsSynchronized Property System.Boolean IsSynchronized

Length Property System.Int32 Length {get;}

LongLength Property System.Int64 LongLength {get;}

Rank Property System.Int32 Rank {get;}

SyncRoot Property System.Object SyncRoot {get;}

As you can see, the Count alias property is listed as one of the properties, with a definition of "Count = Length."

In the types.ps1xml file, you can also define a script property that runs a script against an object's input value. For example, the types.ps1xml file includes a script block that adds the DateTime member to the .NET DateTime object:

<Type>

<Name>System.DateTime</Name>

<Name>DateTime</Name>

if ($this.DisplayHint -ieq "Date")

{

"{0}" -f $this.ToLongDateString()

}

elseif ($this.DisplayHint -ieq "Time")

{

"{0}" -f $this.ToLongTimeString()

}

else

{

"{0} {1}" -f $this.ToLongDateString(),

$this.ToLongTimeString()

}

</GetScriptBlock>

</ScriptProperty>

</Members>

</Type>

The script block formats dates so that different types of values can be used to produce the same results. For example, suppose that you declare the $a variable as shown in the following command:

[datetime]$a = "5 march 05"

PowerShell will convert this value to the following long datetime value:

Saturday, March 05, 2005 12:00:00 AM

You would have received the same results if you had declared that variable with the value "March 5, 2005."

The types.ps1xml can also be used to define property sets. A property set is a set of properties that you can refer to logically as though it were a property itself. For example, PowerShell defines a property set on the DirectoryEntry system type:

<Type>

<Name>System.DirectoryServices.DirectoryEntry</Name>

<Name>PsStandardMembers</Name>

<Name>

DefaultDisplayPropertySet

</Name>

<Name>

distinguishedName

</Name>

</ReferencedProperties>

</PropertySet>

</Members>

</MemberSet>

</Members>

</Type>

In this <type> element, the property set DefaultDisplayPropertySet references the distinguishedName properties.

In addition to modifying the existing types.ps1xml file, you can create your own types.ps1xml file to add type and property definitions or override default type and property definitions. You can then place the new file in any directory in the PowerShell command path. If your file defines a type or property that is already defined, it will replace the same type or property defined in any instance of types.ps1xml that occurs in a directory earlier in the command path.

SEE ALSO

For information about the Get-Member cmdlet, enter the following command:

help Get-Member