Use function pointers interface of static interfaces

src/CSnakes.Runtime/Python/Pack.cs

@@ -5,47 +5,21 @@
 namespace CSnakes.Runtime.Python;
 
 /// <summary>
-/// These methods are used internally to create a PyObject where the Dispose() call will dispose all items in 
+/// These methods are used internally to create a PyObject where the Dispose() call will dispose all items in
 /// the collection inside the same call stack. This avoids the .NET GC Finalizer thread from disposing the items
 /// that were created and creating a GIL contention issue when other code is running.
 /// </summary>
 internal static class Pack
 {
-    internal static PyObject CreateTuple(Span<PyObject> items) =>
-        PyObject.Create(CreateListOrTuple<TupleBuilder>(items));
+    internal static unsafe PyObject CreateTuple(Span<PyObject> items) =>
+        PyObject.Create(CreateListOrTuple(items, &CPythonAPI.PyTuple_New, &CPythonAPI.PyTuple_SetItemRaw));
 
-    internal static PyObject CreateList(Span<PyObject> items) =>
-        PyObject.Create(CreateListOrTuple<ListBuilder>(items));
+    internal static unsafe PyObject CreateList(Span<PyObject> items) =>
+        PyObject.Create(CreateListOrTuple(items, &CPythonAPI.PyList_New, &CPythonAPI.PyList_SetItemRaw));
 
-    public interface IListOrTupleBuilder
-    {
-        static abstract nint New(nint size);
-        static abstract int SetItemRaw(nint ob, nint pos, nint o);
-    }
-
-    public sealed class ListBuilder : IListOrTupleBuilder
-    {
-        // As per Python/C API docs for `PyList_New`:
-        //
-        // > If len is greater than zero, the returned list object's items are set to `NULL`. Thus
-        // > you cannot use abstract API functions such as `PySequence_SetItem()` or expose the
-        // > object to Python code before setting all items to a real object with
-        // > `PyList_SetItem()`.
-        //
-        // Source: https://docs.python.org/3/c-api/list.html#c.PyList_New
-
-        public static IntPtr New(IntPtr size) => CPythonAPI.PyList_New(size);
-        public static int SetItemRaw(IntPtr ob, IntPtr pos, IntPtr o) => CPythonAPI.PyList_SetItemRaw(ob, pos, o);
-    }
-
-    public sealed class TupleBuilder : IListOrTupleBuilder
-    {
-        public static IntPtr New(IntPtr size) => size == 0 ? CPythonAPI.GetPyEmptyTuple() : CPythonAPI.PyTuple_New(size);
-        public static int SetItemRaw(IntPtr ob, IntPtr pos, IntPtr o) => CPythonAPI.PyTuple_SetItemRaw(ob, pos, o);
-    }
-
-    public static nint CreateListOrTuple<TBuilder>(Span<PyObject> items)
-        where TBuilder : IListOrTupleBuilder
+    public static unsafe nint CreateListOrTuple(Span<PyObject> items,
+                                                delegate* <nint, nint> newObject,
+                                                delegate* <nint, nint, nint, int> setItemRaw)
     {
         nint obj = 0;
 
@@ -70,12 +44,12 @@ public static nint CreateListOrTuple<TBuilder>(Span<PyObject> items)
 
             Debug.Assert(uninitializedHandles.Length == 0);
 
-            obj = TBuilder.New(items.Length);
+            obj = newObject(items.Length);
 
             var i = 0;
             foreach (var handle in handles)
             {
-                int result = TBuilder.SetItemRaw(obj, i++, handle);
+                int result = setItemRaw(obj, i++, handle);
                 if (result == -1)
                 {
                     throw PyObject.ThrowPythonExceptionAsClrException();