Enums, Enum values and PowerShell

 

I’ve been reading Jeffrey Snover's discussions on ENUMs over on the PowerShell Team blog (here, and here). I knew most of this stuff and have  been playing with Enums and PowerShell for a while. I’ve created a bunch of sample scripts I’ve uploaded both to the MDSN Wiki and to my PowerShell Scripts blog. This morning, I stumbled upon an interesting use of Enums – parsing strings into Integer values, as shown on the MSDN Library at http://msdn.microsoft.com/en-us/library/system.globalization.numberstyles.aspx.

Effectively want I wanted to do was to convert the following C# code to PowerShell:

1. // Parse the string, allowing a leading sign, and ignoring leading and trailing white spaces. 
2. num = "    -45   "; 
3. val = int.Parse(num, NumberStyles.AllowLeadingSign |  
4.      NumberStyles.AllowLeadingWhite | NumberStyles.AllowTrailingWhite); 
5. Console.WriteLine("'{0}' parsed to an int is '{1}'.", num, val); 

Initially, I could not work out how to use the enums  (In System.Globalization.NumberStyles). Thanks to Shay Levy, it turns out to be remarkably easy (although not quite as succinct as in C'#). Basically, in true PowerShell style, every enum value is just an object. Objects have properties, and one property of an enum value is “value__” as demonstrated here:

PSH [D:\foo]: [System.Globalization.NumberStyles]::AllowLeadingSign
AllowLeadingSign
PSH [D:\foo]: [System.Globalization.NumberStyles]::AllowLeadingSign | gm

   TypeName: System.Globalization.NumberStyles

Name        MemberType   Definition
----        ----------   ----------
CompareTo   Method       System.Int32 CompareTo(Object target)
Equals      Method       System.Boolean Equals(Object obj)
GetHashCode Method       System.Int32 GetHashCode()
GetType     Method       System.Type GetType()
GetTypeCode Method       System.TypeCode GetTypeCode()
ToString    Method       System.String ToString(), System.String ToString(String format, IFormatPr...
value__     Property     System.Int32 value__ {get;set;}
MSDN        ScriptMethod System.Object MSDN();

PSH [D:\foo]: [System.Globalization.NumberStyles]::AllowLeadingSign.value__
4
PSH [D:\foo]:

As you can see from this output, the enum [System.Globalization.NumberStyles]::AllowLeadingSign displays normally the value “AllowLeadingSign” , but if you use the .value__ property on this enum value, you get back a number – in this case a decimal 4 (0x0004). You can then combine these as follows to convert the above C# Code into PowerShell:

1. $num = " -45 "; 
2.   $val = [system.int32]::Parse($num, 
3.                [System.Globalization.NumberStyles]::AllowLeadingSign.value__ + 
4.                [System.Globalization.NumberStyles]::AllowLeadingWhite.value__ + 
5.                [System.Globalization.NumberStyles]::AllowTrailingWhite.value__) 
6. "'{0}' parsed to an int is '{1}'." -f $num, $val 

Thanks to Shay Levy for his post in the PowerShell newsgroup for helping me to work this out. FWIW: you can the results of this up on the MSDN Library and on my PowerShell Scripts blog.

 

Technorati tags: enum, system.globalization.numberstyles, Shay Levy