问题
In PowerShell, you can specify a type with square brackets like so:
PS C:\Users\zippy> [int]
IsPublic IsSerial Name BaseType
-------- -------- ---- --------
True True Int32 System.ValueType
There are also built in type accelerators like [xml] which saves a few keystrokes when you wish to cast something to an XmlDocument.
PS C:\Users\zippy> [xml]
IsPublic IsSerial Name BaseType
-------- -------- ---- --------
True False XmlDocument System.Xml.XmlNode
You can generate the list via one of the two commands:
- PS v2.0
[type]::gettype("System.Management.Automation.TypeAccelerators")::Get - PS v3.0
[psobject].assembly.gettype("System.Management.Automation.TypeAccelerators")::Get
PowerShell 3.0 adds an operator called [ordered]. Its not a type alias though.
PS C:\Users\zippy> [ordered]
Unable to find type [ordered]: make sure that the assembly containing this type is loaded.
At line:1 char:1
+ [ordered]
+ ~~~~~~~~~
+ CategoryInfo : InvalidOperation: (ordered:TypeName) [], RuntimeException
+ FullyQualifiedErrorId : TypeNotFound
However, it can cast Hashtables to OrderedDictionarys.
PS C:\Users\zippy> ([ordered]@{}).GetType()
IsPublic IsSerial Name BaseType
-------- -------- ---- --------
True True OrderedDictionary System.Object
So my question is, if [ordered] is not a type accelerator, what is it?
回答1:
Unfortunately [ordered] is a bit of an aberration. It's neither a type nor an accelerator. It only exists in the parser and is treated as a hint on how to create a hashtable (i.e. don't use hashtable, use ordereddictionary instead.) Think of it as a .net attribute, except it's not :D
回答2:
Using the following command :
Trace-Command -Name TypeConversion -Expression {([ordered]@{}).gettype()} -PSHost
Let me imagine that the interpreter try to match recursively type in loaded assemblies and finished to match OrderedDictionary, this is just a supposition.
来源：https://stackoverflow.com/questions/10238698/what-is-the-proper-name-for-what-ordered-is-in-powershell-3-0