PS (10) > $intList[2].gettype().FullName System.Int32 in C#

Draw Code 39 in C# PS (10) > $intList[2].gettype().FullName System.Int32

Now let s look at another example. This time we ll build a generic dictionary. Instantiating a generic dictionary A generic dictionary is like a hashtable; it s made up of key/value pairs, but we want to limit the keys to strings and the values to integers. Once again, we ll write a convenience function to handle the heavy lifting. Here s the function to do this:

(11) > function New-GenericDictionary ([type] $keyType, [type] $valueType) { $base = [System.Collections.Generic.Dictionary``2] $ct = $base.MakeGenericType(($keyType, $valueType)) , (New-Object $ct) }

Again, start with the base type of the collection, followed by `2 because we have two type parameters this time. We pass the two type parameters to the function into the call to MakeGenericType() as an array. This will give us the closed type for the generic dictionary. Finally, we return an instance of the closed type. We ll use this function to build a dictionary that is constrained to permit only strings for keys and integers for the values.

Let s enter values and display the result:

PS (13) > $gd["red"] = 1 PS (14) > $gd["blue"] = 2 PS (15) > $gd Key --red blue Value ----1 2

Next try to assign a nonstring key. This would work with a regular hashtable, but fails with the generic dictionary instance.

PS (16) > $gd[13] = 3 Array assignment to [13] failed: The value "13" is not of type " System.String" and cannot be used in this generic collection. Parameter name: key. At line:1 char:5 + $gd[1 <<<< 3] = 3

Also note that this time, the PowerShell type converter didn t try to convert to the target type. The type signature is too complex for it to figure out, so we ll have to explicitly cast the arguments. Finally, let s look at the full name of the type of object stored in $gd.

PS (17) > $gd.gettype().FullName System.Collections.Generic.Dictionary`2[[System.String, mscorlib , Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e 089],[System.Int32, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]] PS (18) >

To reiterate the comment from the beginning of this section, very rarely will you need some of these esoteric capabilities, but when you do need them, they can be incredibly valuable. Enough with the .NET trivia challenge. In the remainder of this chapter, we ll look at how we can apply some of the things we ve learned to build more interesting applications.

These examples are designed to demonstrate the range of tasks that can be addressed with PowerShell rather than be strictly practical. For some more purely practical examples using .NET in admin scenarios, take a look at appendix B.

In this section, we re going to put the network back into .NET. As one would expect from a modern programming environment, .NET (and consequently PowerShell) has a pretty comprehensive set of types for doing network programming.

The .NET framework has good networking capabilities, but I suspect that the name came out of the marketing frenzy during the first Internet bubble: .NET 1.0 was released in 2001. At that time, people with calling everything dot-something. I m surprised we didn t end up with .Coke or Pepsi.NET or some other silliness.

In this section, we ll look at a couple useful examples of doing network programming with the .NET networking types. 11.2.1 Example: Retrieving a web page The most common networking task in the Internet age is to download a web page. Here s how to do that in PowerShell using the [system.net.webclient] type. This is a type that provides common methods for sending data to and receiving data from websites (or anything else that can be addressed with a URL). In this example, we ll use this type to download data from the MSDN blog home page. First we need to create an instance of System.Net.WebClient: