[Python.NET] Explicitly implemented interface methods

May 25, 2016

      Hello out there,

I've come across an issue with calling a method of an instance which ends up being an explicitly implemented interface method. Let me explain with a very brief example:

Consider this a very basic interface:

[File: ISomeInterface.cs]
namespace PythonInterfaceCalls
{
    public interface ISomeInterface
    {
        void ImplicitImplementation();
        void ExplicitImplementation();
    }
}

And here's an implementing class. Note one of the methods being implicitly implemented, the other being explicitly implemented:

[File: SomeImplementation.cs]
using System;

namespace PythonInterfaceCalls
{
    public class SomeImplementation: ISomeInterface
    {
        public void ImplicitImplementation()
        {
            Console.WriteLine("Call of implicitly implemented interface method.");
        }

        void ISomeInterface.ExplicitImplementation()
        {
            Console.WriteLine("Call of explicitly implemented interface method.");
        }
    }
}

Note the method headers. While the implicit implementation is (and has to be) public, the explicit implementation is (and has to be) internal. Both methods work well in C# (as long as the instance is casted into the interface type). See the unit tests, both passing:

[File: TestImplementation.cs]
using System;
using System.IO;
using NUnit.Framework;

namespace PythonInterfaceCalls
{
    [TestFixture]
    public class TestImplementation
    {
        [Test]
        public void TestImplicitCall()
        {
            var implementation = new SomeImplementation() as ISomeInterface;
            using (StringWriter sw = new StringWriter())
            {
                Console.SetOut(sw);
                implementation.ImplicitImplementation();
                Assert.AreEqual("Call of implicitly implemented interface method.\r\n", sw.ToString());
            }
        }

        [Test]
        public void TestExplicitCall()
        {
            var implementation = new SomeImplementation() as ISomeInterface;
            using (StringWriter sw = new StringWriter())
            {
                Console.SetOut(sw);
                implementation.ExplicitImplementation();
                Assert.AreEqual("Call of explicitly implemented interface method.\r\n", sw.ToString());
            }
        }
    }
}

This should be solvable using the following method to access all interface members, not just the publicly available ones:

[File: InterfaceMembersExtension.cs]
using System;
using System.Collections.Generic;
using System.Reflection;

namespace PythonInterfaceCalls
{
    public static class InterfaceMembersExtension
    {
        public static IList<MethodInfo> GetImplementedMethods(this Type targetType, Type interfaceType)
        {
            return targetType.GetInterfaceMap(interfaceType).TargetMethods;
        }
    }
}

Please find the complete solution attached to this mail.

Is there a chance that this will be implemented in PythonNet?

Thanks in advance,

Hennnig

[Python.NET] Explicitly implemented interface methods

Henning Moeller