创建通用类的实例

注意：为 PowerShell 5.1 编写的示例你可以创建通用类的实例

#Nullable System.DateTime
[Nullable[datetime]]$nullableDate = Get-Date -Year 2012
$nullableDate
$nullableDate.GetType().FullName
$nullableDate = $null
$nullableDate

#Normal System.DateTime
[datetime]$aDate = Get-Date -Year 2013
$aDate
$aDate.GetType().FullName
$aDate = $null #Throws exception when PowerShell attempts to convert null to 

给出输出：

Saturday, 4 August 2012 08:53:02
System.DateTime
Sunday, 4 August 2013 08:53:02
System.DateTime
Cannot convert null to type "System.DateTime".
At line:14 char:1
+ $aDate = $null
+ ~~~~~~~~~~~~~~
    + CategoryInfo          : MetadataError: (:) [], ArgumentTransformationMetadataException
    + FullyQualifiedErrorId : RuntimeException

通用集合也是可能的

[System.Collections.Generic.SortedDictionary[int, String]]$dict = [System.Collections.Generic.SortedDictionary[int, String]]::new()
$dict.GetType().FullName

$dict.Add(1, 'a')
$dict.Add(2, 'b')
$dict.Add(3, 'c')

$dict.Add('4', 'd') #powershell auto converts '4' to 4
$dict.Add('5.1', 'c') #powershell auto converts '5.1' to 5

$dict

$dict.Add('z', 'z') #powershell can't convert 'z' to System.Int32 so it throws an error

给出输出：

System.Collections.Generic.SortedDictionary`2[[System.Int32, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]

Key Value
--- -----
  1 a
  2 b
  3 c
  4 d
  5 c
Cannot convert argument "key", with value: "z", for "Add" to type "System.Int32": "Cannot convert value "z" to type "System.Int32". Error: "Input string was not in a correct format.""
At line:15 char:1
+ $dict.Add('z', 'z') #powershell can't convert 'z' to System.Int32 so  ...
+ ~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], MethodException
    + FullyQualifiedErrorId : MethodArgumentConversionInvalidCastArgument