Easy Enum Expertise
In this issue:
For today's lesson, I thought we'd explore something you probably use every day in PowerShell, but I doubt you've ever thought about the details, and that is an enumeration. More commonly known as an enum. This is a special .NET class, [System.Enum], that is used throughout PowerShell. I think if you have a better understanding of this class it might help with troubleshooting code. It is also something you can incorporate into your work.
What is an Enum?
In short, an enum is a list of pre-defined and static values. Once defined, the enum values cannot be changed. This ensures that when you use the enum class, the values will be known and predictable. There are two parts to this concept. First, there is the base .NET class which I can discover using the familiar Get-TypeMember command from PSScriptTools.
PS C:\> Get-TypeMember System.Enum
Type: System.Enum
Name MemberType ResultType IsStatic IsEnum
---- ---------- ---------- -------- ------
Format Method String True
GetName Method String True
GetNames Method String[] True
GetType Method Type
GetUnderlyingType Method Type True
GetValues Method TEnum[] True
GetValues Method Array True
GetValuesAsUnderlyingType Method Array True
HasFlag Method Boolean
IsDefined Method Boolean True
Parse Method Object True
Parse Method TEnum True
ToObject Method Object True
ToString Method String
TryFormat Method Boolean True
TryParse Method Boolean True
We can use this class to pick apart the other half of the story, and that is a defined enum. Here is one that I know you are familiar with, although you may not have known it was an enum.
PS C:\> Get-TypeMember System.ConsoleColor
Type: System.ConsoleColor
Name MemberType ResultType IsStatic IsEnum
---- ---------- ---------- -------- ------
Black Field System.ConsoleColor True
Blue Field System.ConsoleColor True
Cyan Field System.ConsoleColor True
DarkBlue Field System.ConsoleColor True
DarkCyan Field System.ConsoleColor True
DarkGray Field System.ConsoleColor True
DarkGreen Field System.ConsoleColor True
DarkMagenta Field System.ConsoleColor True
DarkRed Field System.ConsoleColor True
DarkYellow Field System.ConsoleColor True
Gray Field System.ConsoleColor True
Green Field System.ConsoleColor True
Magenta Field System.ConsoleColor True
Red Field System.ConsoleColor True
White Field System.ConsoleColor True
Yellow Field System.ConsoleColor True
GetType Method Type
HasFlag Method Boolean
ToString Method String
The fields reflect the defined members of the enum.
> The IsEnum property is used to show if a class property is an enum. You'll see that later.
One way to test if a class is an enum is by checking the isEnum property.
PS C:\> [ConsoleColor].IsEnum
True
Enum Names
When it comes to identifying the names in the enum, we have a few options, beyond using Get-TypeMember. You can use PSReadline. Start typing the class name followed by :: and then Ctrl+Space.
Or just press Tab after the ::.
You can use the [Enum] class.
PS C:\> [Enum]::GetNames([ConsoleColor])
Black
DarkBlue
DarkGreen
DarkCyan
DarkRed
DarkMagenta
DarkYellow
Gray
DarkGray
Blue
Green
Cyan
Red
Magenta
Yellow
White
Any enum class inherits this method, so you could also do this:
PS C:\> [ConsoleColor]::GetNames([ConsoleColor])
Black
DarkBlue
DarkGreen
DarkCyan
DarkRed
DarkMagenta
DarkYellow
Gray
DarkGray
Blue
Green
Cyan
Red
Magenta
Yellow
White
