We see that $b was in fact not changed. Conversely, changing $b should have no effect on $a. in Visual C#.NET

Creating ANSI/AIM Code 39 in Visual C#.NET We see that $b was in fact not changed. Conversely, changing $b should have no effect on $a.

Again, there was no change. To reiterate, arrays in PowerShell, like arrays in other .NET languages, are reference types, not value types. When you assign them to a variable, you get another reference to the array, not another copy of the array. Singleton arrays and empty arrays Returning to array literals, we saw how to use the comma operator to build up an array containing more than one element. You also use the comma operator as a prefix operator to create an array containing only one element. The next example shows this:

In the example we made an array containing a single element 1 . How about empty arrays The comma operator always takes an argument to work on. Even using $null as an argument to the comma operator will result in a one-element array containing the $null reference. Empty arrays are created through a special form of sub-expression notation that uses the @ symbol instead of the $ sign to start the expression. Here s what it looks like:

In the preceding example, we created an array of length 0. In fact, this notation is more general. It takes the result of the expression it encloses and ensures that it is always returned as an array. If the expression returns $null or a scalar value, it will be wrapped in a one-element array. Given this behavior, the other solution to creating an array with one element is:

That is, you place the value you want in the array in @( ... ) and you get an array back. This notation is used when you don t know if the command you re calling is going to return an array or not. By executing the command in this way, you are guaranteed to get an array back. Note that if what you re returning is already an array, it won t be wrapped in a new array. Compare this to the use of the comma operator.

PS 1 2 3 PS 3 PS 1 PS 3 (1) > 1,2,3

On line 1 of the example, we created a regular array. On line 5, we get the length and we see that it s 3. Next on line 7, we apply the prefix operator to the array and then get the length. The result now is only 1. This is because the unary comma operator always wraps its arguments in a new array. Finally, on line 9, we use the @( ... ) notation and then get the length. This time it remains three. The @( ... ) sequence doesn t wrap unless the object is not an array. 3.2.5 Type literals In earlier sections, we showed a number of things that looked like [type]. These are type literals. In PowerShell, you use type literals to specify a particular type. They can be used as operators in a cast, as part of a variable declaration, or as an object itself. Here s an example of a cast using a type literal:

$i = [int] "123"

In this example, we are casting a string into a number, specifically an instance of primitive .NET type System.Int32. In fact, we could use the longer .NET type name to accomplish this:

$i = [System.Int32] "123"

It would be useful to try something more sophisticated. If we wanted to make this into an array of integers, we would do

$i = [int[]][object[]] "123"

In this example, we re not just casting the base type, we re also changing it from a scalar object to an array. Notice that we had to do this in two steps. In the first step, we converted it into a collection but without changing the element type. In the second step, we convert the types of the individual elements. This follows the general type converter rule that no more than one conversion will be performed in a single step. This rule makes it much easier to predict what any given conversion will do. Type name aliases Obviously, the shorter type name (or type alias as it s known) is more convenient. Table 3.4 lists all of the type aliases defined in PowerShell and the .NET types they correspond to. Anything in the System.Management.Automation namespace is specific to PowerShell and will be covered in later chapters in this book. The other types are core .NET types and are covered in the Microsoft Developers Network documentation.

Table 3.4 PowerShell type aliases and their corresponding .NET types Corresponding .NET Type System.Int32 System.Int32[] System.Int64 System.Int64[] System.String System.String[] System.Char System.Char[] System.Boolean System.Boolean[] System.Byte System.Byte[] System.Double System.Double[] System.Decimal System.Decimal[] System.Single continued on next page

PowerShell Type Alias [int] [int[]] [long] [long[]] [string] [string[]] [char] [char[]] [bool] [bool[]] [byte] [byte[]] [double] [double[]] [decimal] [decimal[] [float]