Calling generic static method in PowerShell

Question

How do you call a generic static method of a custom class in Powershell?

Given the following class:

public class Sample {     public static string MyMethod<T>( string anArgument )     {         return string.Format( "Generic type is {0} with argument {1}", typeof(T), anArgument );     } } 

And this is compiled into an assembly 'Classes.dll' and loaded into PowerShell like this:

Add-Type -Path "Classes.dll" 

What's the easiest way to call the MyMethod method?

Answer 1

The easiest way to call MyMethod is, as @Athari says, to use MakeGenericMethod. Since he doesn't actually show how to do that, here is a verified working code sample:

$obj = New-Object Sample  $obj.GetType().GetMethod("MyMethod").MakeGenericMethod([String]).Invoke($obj, "Test Message") $obj.GetType().GetMethod("MyMethod").MakeGenericMethod([Double]).Invoke($obj, "Test Message") 

with output

Generic type is System.String with argument Test Message Generic type is System.Double with argument Test Message 

Answer 2

You can call generic methods, refer to the post Invoking Generic Methods on Non-Generic Classes in PowerShell.

This is not straightforward, you need to use MakeGenericMethod function. It is pretty simple if method doesn't have overrides, it gets harder if it does.

Just in case, copy-pasted code from there:

## Invoke-GenericMethod.ps1  ## Invoke a generic method on a non-generic type:  ##  ## Usage:  ##  ##   ## Load the DLL that contains our class ##   [Reflection.Assembly]::LoadFile("c:\temp\GenericClass.dll") ## ##   ## Invoke a generic method on a non-generic instance ##   $nonGenericClass = New-Object NonGenericClass ##   Invoke-GenericMethod $nonGenericClass GenericMethod String "How are you?" ## ##   ## Including one with multiple arguments ##   Invoke-GenericMethod $nonGenericClass GenericMethod String ("How are you?",5) ## ##   ## Ivoke a generic static method on a type ##   Invoke-GenericMethod ([NonGenericClass]) GenericStaticMethod String "How are you?" ##   param(     $instance = $(throw "Please provide an instance on which to invoke the generic method"),     [string] $methodName = $(throw "Please provide a method name to invoke"),     [string[]] $typeParameters = $(throw "Please specify the type parameters"),     [object[]] $methodParameters = $(throw "Please specify the method parameters")     )   ## Determine if the types in $set1 match the types in $set2, replacing generic ## parameters in $set1 with the types in $genericTypes function ParameterTypesMatch([type[]] $set1, [type[]] $set2, [type[]] $genericTypes) {     $typeReplacementIndex = 0     $currentTypeIndex = 0      ## Exit if the set lengths are different     if($set1.Count -ne $set2.Count)     {         return $false     }      ## Go through each of the types in the first set     foreach($type in $set1)     {         ## If it is a generic parameter, then replace it with a type from         ## the $genericTypes list         if($type.IsGenericParameter)         {             $type = $genericTypes[$typeReplacementIndex]             $typeReplacementIndex++         }          ## Check that the current type (i.e.: the original type, or replacement         ## generic type) matches the type from $set2         if($type -ne $set2[$currentTypeIndex])         {             return $false         }         $currentTypeIndex++     }      return $true }  ## Convert the type parameters into actual types [type[]] $typedParameters = $typeParameters  ## Determine the type that we will call the generic method on. Initially, assume ## that it is actually a type itself. $type = $instance  ## If it is not, then it is a real object, and we can call its GetType() method if($instance -isnot "Type") {     $type = $instance.GetType() }  ## Search for the method that: ##    - has the same name ##    - is public ##    - is a generic method ##    - has the same parameter types foreach($method in $type.GetMethods()) {     # Write-Host $method.Name     if(($method.Name -eq $methodName) -and     ($method.IsPublic) -and     ($method.IsGenericMethod))     {         $parameterTypes = @($method.GetParameters() | % { $_.ParameterType })         $methodParameterTypes = @($methodParameters | % { $_.GetType() })         if(ParameterTypesMatch $parameterTypes $methodParameterTypes $typedParameters)         {             ## Create a closed representation of it             $newMethod = $method.MakeGenericMethod($typedParameters)              ## Invoke the method             $newMethod.Invoke($instance, $methodParameters)              return         }     } }  ## Return an error if we couldn't find that method throw "Could not find method $methodName"