Can we implement .NET interfaces in PowerShell scripts?

Question

Lets say we have a few interfaces defined in a .NET class library written in C#. Is there a way to implement these interfaces in a PowerShell script?

Call this a business need. We as a vendor, provide a few interfaces that are implemented by our customers to use our product. One of our customer wants to do this from PowerShell script.

Answer 1

Here's a simple example with PowerShell 5.0 implementing the .Net IEqualityComparer interface:

Class A:System.Collections.IEqualityComparer {
  [bool]Equals($x,$y)  { return $x -eq $y        }
  [int]GetHashCode($x) { return $x.GetHashCode() }
}
[A]$a=[A]::new()
$a.Equals(1,1) -- returns True
$a.Equals(1,2) -- returns False
$a.GetHashCode("OK") -- returns 2041362128

You could even have a class (called A), which inherits from another class (called B) and implements IEqualityComparer:

Class A:B,System.Collections.IEqualityComparer {

Answer 2

You can use Add-Type to define the class in C#, JScript, or VBScript. When there's a vendor-supplied assembly involved, it just has to be loaded prior to the Add-Type call, with another call to Add-Type:

$sourceCode = @"
    public class CustomerClass : Vendor.Interface
    {
         public bool BooleanProperty { get; set; }
         public string StringProperty { get; set; }
    }
"@    # this here-string terminator needs to be at column zero

$assemblyPath = 'C:\Path\To\Vendor.dll'
Add-Type -LiteralPath $assemblyPath
Add-Type -TypeDefinition $sourceCode -Language CSharp -ReferencedAssemblies $assemblyPath

$object = New-Object CustomerClass
$object.StringProperty = "Use the class"

Answer 3

EDIT: It seems you can now implement interfaces in powershell 5.0. This answer applies to powershell 4.0 or earlier.

Although you cannot implement interface from powershell directly, you can pass powershell delegates to .NET code. You could provide empty implementation of interface accepting delegates in constructor, and construct this object from powershell:

public interface IFoo
{
    void Bar();
}

public class FooImpl : IFoo
{
    Action bar_;
    public FooImpl(Action bar)
    {
        bar_ = bar;
    }

    public void Bar()
    {
        bar_();
    }
}

And in powershell:

$bar = 
{ 
   Write-Host "Hello world!"
}

$foo = New-Object FooImpl -ArgumentList $bar
# pass foo to other .NET code