From a10de60f71f38edbc9e8849db04d6c66f3d0dece Mon Sep 17 00:00:00 2001
From: Daniel Abrahamsson <daniel.abrahamsson@prover.com>
Date: Mon, 12 Oct 2020 13:52:39 +0200
Subject: [PATCH] Return interface objects when iterating over interface
 collections

---
 src/runtime/classbase.cs    | 19 +++++++++++++++++--
 src/runtime/iterator.cs     |  6 ++++--
 src/tests/test_interface.py | 16 ++++++++++++++++
 3 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/src/runtime/classbase.cs b/src/runtime/classbase.cs
index 66153fbe1..09adf5afe 100644
--- a/src/runtime/classbase.cs
+++ b/src/runtime/classbase.cs
@@ -1,5 +1,6 @@
 using System;
 using System.Collections;
+using System.Collections.Generic;
 using System.Diagnostics;
 using System.Runtime.InteropServices;
 using System.Runtime.Serialization;
@@ -184,7 +185,6 @@ public static IntPtr tp_iter(IntPtr ob)
 
             var e = co.inst as IEnumerable;
             IEnumerator o;
-
             if (e != null)
             {
                 o = e.GetEnumerator();
@@ -199,7 +199,22 @@ public static IntPtr tp_iter(IntPtr ob)
                 }
             }
 
-            return new Iterator(o).pyHandle;
+            var elemType = typeof(object);
+            var iterType = co.inst.GetType();
+            foreach(var ifc in iterType.GetInterfaces())
+            {
+                if (ifc.IsGenericType)
+                {
+                    var genTypeDef = ifc.GetGenericTypeDefinition();
+                    if (genTypeDef == typeof(IEnumerable<>) || genTypeDef == typeof(IEnumerator<>))
+                    {
+                        elemType = ifc.GetGenericArguments()[0];
+                        break;
+                    }
+                }
+            }
+
+            return new Iterator(o, elemType).pyHandle;
         }
 
 
diff --git a/src/runtime/iterator.cs b/src/runtime/iterator.cs
index f9cf10178..089e8538a 100644
--- a/src/runtime/iterator.cs
+++ b/src/runtime/iterator.cs
@@ -10,10 +10,12 @@ namespace Python.Runtime
     internal class Iterator : ExtensionType
     {
         private IEnumerator iter;
+        private Type elemType;
 
-        public Iterator(IEnumerator e)
+        public Iterator(IEnumerator e, Type elemType)
         {
             iter = e;
+            this.elemType = elemType;
         }
 
 
@@ -41,7 +43,7 @@ public static IntPtr tp_iternext(IntPtr ob)
                 return IntPtr.Zero;
             }
             object item = self.iter.Current;
-            return Converter.ToPythonImplicit(item);
+            return Converter.ToPython(item, self.elemType);
         }
 
         public static IntPtr tp_iter(IntPtr ob)
diff --git a/src/tests/test_interface.py b/src/tests/test_interface.py
index e6c6ba64b..4546471f2 100644
--- a/src/tests/test_interface.py
+++ b/src/tests/test_interface.py
@@ -120,3 +120,19 @@ def test_implementation_access():
     assert 100 == i.__implementation__
     assert clrVal == i.__raw_implementation__
     assert i.__implementation__ != i.__raw_implementation__
+
+
+def test_interface_collection_iteration():
+    """Test interface type is used when iterating over interface collection"""
+    import System
+    from System.Collections.Generic import List
+    elem = System.IComparable(System.Int32(100))
+    typed_list = List[System.IComparable]()
+    typed_list.Add(elem)
+    for e in typed_list:
+        assert type(e).__name__ == "IComparable"
+
+    untyped_list = System.Collections.ArrayList()
+    untyped_list.Add(elem)
+    for e in untyped_list:
+        assert type(e).__name__ == "int"