How to use delegates inside a static PowerShell class?

Question

I want to use a func delegate in my static PowerShell 5.0 class:

I had issues to find a way to assign other static class methods for my delegate.

This code is working but not very convinient.

Is there a better way to use a delegate here ?

And I need to instanciate my static! class, only to get the type.

I tried the outcommented line, how you would do it with .NET types, but it's not working for my own class.

How can I get the type of my static class here more elegant ?

And, BTW, GetMethod() did not accecpt the BindingFlags parameter, why ?

class Demo
{
    hidden static [object] Method_1([string] $myString)
    {
        Write-Host "Method_1: $myString"
        return "something"    
    }

    hidden static [object] Method_2([string] $myString)
    {
        Write-Host "Method_2: $myString"    
        return $null    
    }

    hidden static [object] TheWrapper([string]$wrappedMethod, [string] $parameter)
    {
        # do a lot of other stuff here... 

        #return [System.Type]::GetType("Demo").GetMethod($wrappedMethod).CreateDelegate([Func``2[string, object]]).Invoke($parameter)
        return [Demo]::new().GetType().GetMethod($wrappedMethod).CreateDelegate([Func``2[string, object]]).Invoke($parameter)    
    }

    static DoWork()
    {
        Write-Host ([Demo]::TheWrapper('Method_1', 'MyMessage'))
        [Demo]::TheWrapper('Method_2', 'c:\my_file.txt')
    }
}

[Demo]::DoWork()

[Demo]::new().GetType() -> [Demo]

user4003407
– user4003407

2018-05-16 23:12:44 +00:00
Commented May 16, 2018 at 23:12 — user4003407
– user4003407, Commented May 16, 2018 at 23:12
first question answered, Thanks :-)

andiDo
– andiDo

2018-05-16 23:24:13 +00:00
Commented May 16, 2018 at 23:24 — andiDo
– andiDo, Commented May 16, 2018 at 23:24

Bruce Payette · Accepted Answer · 2018-05-17 00:03:31Z

1

You don't need to create an instance of [demo] since [demo] is the actual type of the class. Also, you can write the delegate type more simply as [Func[string,object]]. This simplifies the body of TheWrapper method to

return [Demo].GetMethod($wrappedMethod).CreateDelegate([Func[string, object]]).Invoke($parameter)

but a much simpler way to do this in PowerShell is to get the method by passing its name to the '.' operator then invoking the result:

return [demo]::$wrappedMethod.Invoke($parameter)

In PowerShell, the right-hand side of the '.' operator doesn't need to be a constant. You can use an expression that results in the name of the method (or property) to retrieve.

answered May 17, 2018 at 0:03

Bruce Payette

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2 Comments

user4003407 Over a year ago

Is any particular reason to use [demo]::$wrappedMethod.Invoke($parameter) over [demo]::$wrappedMethod($parameter)?

andiDo Over a year ago

Thank you so much :-) I always forget how simple you can achive such things in script languages, but isn't it a safer way to explicitly use a C# delegate ?

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