In Powershell, how do I make use of byte array as key type to one of my C# Generic class please?

Question

I have C# class in an external DLL which I cannot modify. Two of the classes in the library are defined as follows which I need to use in my Powershell script.

public class MyCsharpClass<TKey, TValue> : ISomeBaseClass<TKey, TValue>
{
    public MyCsharpClass(string path, ISomeBaseTranslator<TKey, TValue> translator)
    {
        ...
    }
}
...
...
public class MyByteTranslatorCSharpClass: ISomeBaseTranslator<byte[], byte[]>
{
    ...
}

I want to create instance of MyCsharpClass in Powershell script as follows:

$MyType = [MyCsharpClass[byte[],byte[]]]::new($Path, [MyByteTranslatorCSharpClass]::new())

But the above line fails with below error. I can just enter type name in PS ISE command window and get the same error.

PS C:\> [MyCsharpClass[byte[],byte[]]]
At line:1 char:30
+ [MyCsharpClass[byte[],byte[]]]
+                                                                     ~
Unexpected token ']' in expression or statement.
    + CategoryInfo          : ParserError: (:) [], ParentContainsErrorRecordException
    + FullyQualifiedErrorId : UnexpectedToken

Below line works fine though showing me the type info of my class when I just use byte type for TKey:

PS C:\> [MyCsharpClass[byte,byte[]]]

IsPublic IsSerial Name                                     BaseType                                                                                                                                         
-------- -------- ----                                     --------                                                                                                                                         
True     False    MyCsharpClass                           System.Object

It seems the first closing bracket ']' for my Key type of byte[] confuses Powershell that type definition is being closed and so it raises error when it observes Unexpected token ']' in the end of expression.

I also tried to replace byte[] type with System.Collections.Generic.List type which works fine now for declaring a type.

PS C:\> MyCsharpClass[System.Collections.Generic.List[System.Byte],System.Collections.Generic.List[System.Byte]]]

IsPublic IsSerial Name                                     BaseType                                                                                                                                         
-------- -------- ----                                     --------                                                                                                                                         
True     False    MyCsharpClass                           System.Object

However the constructor invocation fails this time while passing instance of MyByteTranslatorCSharpClass as second argument in constructor (at the end of below line).

$MyType = [MyCsharpClass[System.Collections.Generic.List[System.Byte],System.Collections.Generic.List[System.Byte]]]::new($Path, [MyByteTranslatorCSharpClass]::new())

This gives exception of 'System.Management.Automation.MethodException: Cannot convert argument "translator", with value: "MyByteTranslatorCSharpClass", for ".ctor" to type "ISomeBaseTranslator[System.Collections.Generic.List1[System.Byte],System.Collections.Generic.List1[System.Byte]]"

Please let me know in this context, how can I create instance of MyCsharpClass with byte[] type for TKey and TValue generic arguments in Powershell. Please note that I can neither change the DLL side nor do I have its source.

Mathias R. Jessen · Accepted Answer · 2020-05-29 22:28:18Z

3

This appears to be a type name parsing bug.

Fortunately, you can easily work around this by "qualifying" the type parameter literals with an extra pair of square brackets ([]) :

[MyCsharpClass[[byte[]],[byte[]]]]::new(...)

... or by constructing the concrete type directly using reflection:

$myType = [MyCsharpClass`2].MakeGenericType(@([byte[]],[byte[]]))

$myType::new(...)

answered May 29, 2020 at 22:28

Mathias R. Jessen

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1 Comment

Vishwanath Kamath Over a year ago

Thanks for the quick response :)

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