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ABOUT ENUM
SHORT DESCRIPTION
The enum statement is used to declare an enumeration. An enumeration is a
distinct type that consists of a set of named labels called the enumerator
list.
LONG DESCRIPTION
The enum statement allows you to create a strongly typed set of labels.
That enumeration can be used in the code without having to parse or check
for spelling errors.
Enumerations are internally represented as integers with a starting value
of zero. The first label in the list is assigned the value zero. The
remaining labels are assigned with consecutive numbers.
In the definition, labels can be given any integer value. Labels with no
value assigned take the next integer value.
Syntax (basic)
enum <enum-name> {
<label> [= <int-value>]
...
}
Usage example
The following example shows an enumeration of objects that can be seen as
media files. The definition assigns explicit values to the underlying
values of music, picture, video. Labels immediately following an explicit
assignment get the next integer value. Synonyms can be created by assigning
the same value to another label; see the constructed values for: ogg, oga,
mogg, or jpg, jpeg, or mpg, mpeg.
enum MediaTypes {
unknown
music = 10
mp3
aac
ogg = 15
oga = 15
mogg = 15
picture = 20
jpg
jpeg = 21
png
video = 40
mpg
mpeg = 41
avi
m4v
}
The GetEnumNames() method returns the list of the labels for the
enumeration.
[MediaTypes].GetEnumNames()
unknown
music
mp3
aac
ogg
oga
mogg
picture
jpg
jpeg
png
video
mpg
mpeg
avi
m4v
The GetEnumValues() method returns the list of the values for the
enumeration.
[MediaTypes].GetEnumValues()
unknown
music
mp3
aac
oga
oga
oga
picture
jpeg
jpeg
png
video
mpeg
mpeg
avi
m4v
NOTE: GetEnumNames() and GetEnumValues() seem to return the same results.
However, internally, PowerShell is changing values into labels. Read the
list carefully and you'll notice that oga and mogg are mentioned under the
'Get Names' results, but not under the 'Get Values' similar output for jpg,
jpeg, and mpg, mpeg.
[MediaTypes].GetEnumName(15)
oga
[MediaTypes].GetEnumNames() | ForEach-Object {
"{0,-10} {1}" -f $_,[int]([MediaTypes]::$_)
}
unknown 0
music 10
mp3 11
aac 12
ogg 15
oga 15
mogg 15
picture 20
jpg 21
jpeg 21
png 22
video 40
mpg 41
mpeg 41
avi 42
m4v 43
Enumerations as flags
Enumerations can be defined as a collection of bit flags. Where, at any
given point the enumeration represents one or more of those flags turned
on.
For enumerations as flags to work properly, each label should have a power
of two value.
Syntax (flags)
[Flags()] enum <enum-name> {
<label 0> [= 1]
<label 1> [= 2]
<label 2> [= 4]
<label 3> [= 8]
...
}
Flags usage example
In the following example the _FileAttributes_ enumeration is created.
[Flags()] enum FileAttributes {
Archive = 1
Compressed = 2
Device = 4
Directory = 8
Encrypted = 16
Hidden = 32
}
[FileAttributes]$file1 = [FileAttributes]::Archive
[FileAttributes]$file1 +=[FileAttributes]::Compressed
[FileAttributes]$file1 += [FileAttributes]::Device
"file1 attributes are: $file1"
[FileAttributes]$file2 = [FileAttributes]28 ## => 16 + 8 + 4
"file2 attributes are: $file2"
file1 attributes are: Archive, Compressed, Device
file2 attributes are: Device, Directory, Encrypted
To test that a specific is set, you can use the binary comparison operator
-band. In this example, we test for the DEVICE and the ARCHIVE attributes
in the value of $file2.
PS > ($file2 -band [FileAttributes]::Device) -eq [FileAttributes]::Device
True
PS > ($file2 -band [FileAttributes]::Archive) -eq [FileAttributes]::Archive
False