call C# method from powershell without supplying optional arguments

Question

I have a c# method I am loading from a dll with optional string arguments that default to null. For example

public void foo(string path, string new_name = null, bool save_now = true)
{
    if(name == null)
        new_name = Path.GetFileNameWithoutExtension(path);
    ...
    if(save_now)
       Save();
}

I want to call this from within a powershell script and not supply a value for new_name but one for save_now. As per this seemingly very similar question I have tried

$default = [type]::Missing
$obj.foo($path, $default, $false)

but this results in new_name being set as "System.Reflection.Missing" within the function.

Additionally I tried

$obj.foo($path, $null, $false)

but this results in new_name being set to the empty string, still not null. I could set the default to the empty string, but I was wondering if there was any good way to actually have the default value be used.

Answer 1

No can do in PowerShell. It doesn't support C#/VB optional parameters. It is the duty of the language calling the method to provide the default values when the programmer doesn't and PowerShell just doesn't do that.

Answer 2

You can simply omit the optional parameters in the call. I modified your example to run it in PS. For example:

$c = @"
    public static class Bar {
        public static void foo(string path, string new_name = null, bool save_now = true)
        {
            System.Console.WriteLine(path);
            System.Console.WriteLine(new_name);
            System.Console.WriteLine(save_now);
        }
    }
"@

add-type -TypeDefinition $c

[Bar]::Foo("test",[System.Management.Automation.Language.NullString]::Value,$false)

This generates the following

test
False

Test was passed explicitly, null is null and had no output, and the save_now evaluated to the default of True.