From 1b7fe15ca33436411dffd8d7d59e1ecea27b964b Mon Sep 17 00:00:00 2001
From: Jay Dolan <jay@jaydolan.com>
Date: Wed, 2 Sep 2026 19:17:14 -0400
Subject: [PATCH 1/5] Resolve interfaces through Class, not per-instance
 pointers

Every instance struct carried its own copy of the interface pointer, one per level
of its hierarchy, all holding the same value: clazz->interface. _alloc walked the
superclass chain writing that pointer into each level's slot, and every ClassDef
had to supply interfaceOffset to say where the slot was.

The `$` macro never needed the stored value, only its type. The member is now a
zero-length array, which carries the type for `typeof` and occupies no storage.
`$` resolves the interface through Object::clazz on every call. interfaceOffset
and the _alloc loop are gone. No call site changes.

Because dispatch, cast, and isKindOfClass now all read the same field, reassigning
clazz after allocation is sound: type checks and behavior change together. That
permits Classes minted purely for behavior over an existing instance layout, which
is what #23 asked for.

Refs #23

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
---
 .github/copilot-instructions.md               | 10 +++---
 .github/copilot/skills/new-type.md            |  3 +-
 Documentation/guide.md                        | 35 ++++++++++++++++---
 Examples/Hello.c                              |  1 -
 Examples/Hello.h                              |  4 +--
 Sources/Objectively/Array.c                   |  1 -
 Sources/Objectively/Array.h                   |  4 +--
 Sources/Objectively/Boole.c                   |  1 -
 Sources/Objectively/Boole.h                   |  4 +--
 Sources/Objectively/Class.c                   |  6 ----
 Sources/Objectively/Class.h                   | 20 +++++++----
 Sources/Objectively/Condition.c               |  1 -
 Sources/Objectively/Condition.h               |  4 +--
 Sources/Objectively/Data.c                    |  1 -
 Sources/Objectively/Data.h                    |  4 +--
 Sources/Objectively/Date.c                    |  1 -
 Sources/Objectively/Date.h                    |  4 +--
 Sources/Objectively/DateFormatter.c           |  1 -
 Sources/Objectively/DateFormatter.h           |  4 +--
 Sources/Objectively/Dictionary.c              |  1 -
 Sources/Objectively/Dictionary.h              |  4 +--
 Sources/Objectively/Error.c                   |  1 -
 Sources/Objectively/Error.h                   |  4 +--
 Sources/Objectively/HashTable.c               |  1 -
 Sources/Objectively/HashTable.h               |  4 +--
 Sources/Objectively/IndexPath.c               |  1 -
 Sources/Objectively/IndexPath.h               |  4 +--
 Sources/Objectively/IndexSet.c                |  1 -
 Sources/Objectively/IndexSet.h                |  4 +--
 Sources/Objectively/JSONContext.c             |  1 -
 Sources/Objectively/JSONContext.h             |  4 +--
 Sources/Objectively/JSONPath.c                |  1 -
 Sources/Objectively/JSONPath.h                |  4 +--
 Sources/Objectively/List.c                    |  1 -
 Sources/Objectively/List.h                    |  4 +--
 Sources/Objectively/Lock.c                    |  1 -
 Sources/Objectively/Lock.h                    |  4 +--
 Sources/Objectively/Log.c                     |  1 -
 Sources/Objectively/Log.h                     |  4 +--
 Sources/Objectively/Null.c                    |  1 -
 Sources/Objectively/Null.h                    |  4 +--
 Sources/Objectively/Number.c                  |  1 -
 Sources/Objectively/Number.h                  |  4 +--
 Sources/Objectively/NumberFormatter.c         |  1 -
 Sources/Objectively/NumberFormatter.h         |  4 +--
 Sources/Objectively/Object.c                  |  1 -
 Sources/Objectively/Object.h                  |  4 +--
 Sources/Objectively/Operation.c               |  1 -
 Sources/Objectively/Operation.h               |  4 +--
 Sources/Objectively/OperationQueue.c          |  1 -
 Sources/Objectively/OperationQueue.h          |  4 +--
 Sources/Objectively/Pointer.c                 |  1 -
 Sources/Objectively/Pointer.h                 |  4 +--
 Sources/Objectively/PointerArray.c            |  1 -
 Sources/Objectively/PointerArray.h            |  4 +--
 Sources/Objectively/RESTClient.c              |  1 -
 Sources/Objectively/RESTClient.h              |  4 +--
 Sources/Objectively/Regexp.c                  |  1 -
 Sources/Objectively/Regexp.h                  |  4 +--
 Sources/Objectively/Resource.c                |  1 -
 Sources/Objectively/Resource.h                |  4 +--
 Sources/Objectively/Set.c                     |  1 -
 Sources/Objectively/Set.h                     |  4 +--
 Sources/Objectively/String.c                  |  1 -
 Sources/Objectively/String.h                  |  4 +--
 Sources/Objectively/StringReader.c            |  1 -
 Sources/Objectively/StringReader.h            |  4 +--
 Sources/Objectively/Thread.c                  |  1 -
 Sources/Objectively/Thread.h                  |  4 +--
 Sources/Objectively/URL.c                     |  1 -
 Sources/Objectively/URL.h                     |  4 +--
 Sources/Objectively/URLCache.c                |  1 -
 Sources/Objectively/URLCache.h                |  4 +--
 Sources/Objectively/URLCachedResponse.c       |  1 -
 Sources/Objectively/URLCachedResponse.h       |  4 +--
 Sources/Objectively/URLRequest.c              |  1 -
 Sources/Objectively/URLRequest.h              |  4 +--
 Sources/Objectively/URLResponse.c             |  1 -
 Sources/Objectively/URLResponse.h             |  4 +--
 Sources/Objectively/URLSession.c              |  1 -
 Sources/Objectively/URLSession.h              |  4 +--
 Sources/Objectively/URLSessionConfiguration.c |  1 -
 Sources/Objectively/URLSessionConfiguration.h |  4 +--
 Sources/Objectively/URLSessionDataTask.c      |  1 -
 Sources/Objectively/URLSessionDataTask.h      |  4 +--
 Sources/Objectively/URLSessionDownloadTask.c  |  1 -
 Sources/Objectively/URLSessionDownloadTask.h  |  4 +--
 Sources/Objectively/URLSessionTask.c          |  1 -
 Sources/Objectively/URLSessionTask.h          |  4 +--
 Sources/Objectively/URLSessionUploadTask.c    |  1 -
 Sources/Objectively/URLSessionUploadTask.h    |  4 +--
 Sources/Objectively/Vector.c                  |  1 -
 Sources/Objectively/Vector.h                  |  4 +--
 Templates/Eclipse/eclipse-code-templates.xml  |  5 ++-
 .../___FILEBASENAME___.c                      |  1 -
 .../___FILEBASENAME___.h                      |  4 +--
 96 files changed, 142 insertions(+), 162 deletions(-)

diff --git a/.github/copilot-instructions.md b/.github/copilot-instructions.md
index d6aaa0b..2ef6339 100644
--- a/.github/copilot-instructions.md
+++ b/.github/copilot-instructions.md
@@ -29,14 +29,15 @@ Tests use [libcheck](https://libcheck.github.io/check/). Each test file has its
 
 Every Objectively type consists of exactly three pieces:
 
-1. **Instance struct** (`Foo.h`) — starts with the parent type, then the interface pointer, then instance variables:
+1. **Instance struct** (`Foo.h`) — starts with the parent type, then the zero-length interface member, then instance variables:
    ```c
    struct Foo {
-     Bar bar;               // parent (starts-with composition = single inheritance)
-     FooInterface *interface;
+     Bar bar;                    // parent (starts-with composition = single inheritance)
+     FooInterface *interface[0]; // carries a type, occupies no storage; `$` reads it via typeof
      int myField;
    };
    ```
+   The `interface` member MUST directly follow the parent: it has pointer alignment, so placing it after a smaller field would introduce padding.
 
 2. **Interface struct** (`Foo.h`) — starts with the parent interface, then method function pointers:
    ```c
@@ -58,7 +59,7 @@ The `.c` file contains `static` implementations, an `initialize` function that w
 
 ### Dispatch macros
 ```c
-$(obj, method, args)          // instance method dispatch (obj->interface->method)
+$(obj, method, args)          // instance method dispatch (classof(obj)->interface->method)
 $$(Type, method, args)        // class/static method dispatch
 super(Type, obj, method, args) // call superclass implementation
 alloc(Type)                   // allocate an instance
@@ -95,7 +96,6 @@ Class *_Foo(void) {
       .name = "Foo",
       .superclass = _Bar(),
       .instanceSize = sizeof(Foo),
-      .interfaceOffset = offsetof(Foo, interface),
       .interfaceSize = sizeof(FooInterface),
       .initialize = initialize,
     });
diff --git a/.github/copilot/skills/new-type.md b/.github/copilot/skills/new-type.md
index a58e8b0..75798bf 100644
--- a/.github/copilot/skills/new-type.md
+++ b/.github/copilot/skills/new-type.md
@@ -19,7 +19,7 @@ typedef struct FooInterface FooInterface;
 
 struct Foo {
   Bar bar;                     // parent first (starts-with inheritance)
-  FooInterface *interface;
+  FooInterface *interface[0];  // zero-length: carries a type for `$`, no storage; MUST follow the parent
   // instance variables...
 };
 
@@ -82,7 +82,6 @@ Class *_Foo(void) {
       .name = "Foo",
       .superclass = _Bar(),
       .instanceSize = sizeof(Foo),
-      .interfaceOffset = offsetof(Foo, interface),
       .interfaceSize = sizeof(FooInterface),
       .initialize = initialize,
     });
diff --git a/Documentation/guide.md b/Documentation/guide.md
index b37fd4c..50e8b0b 100644
--- a/Documentation/guide.md
+++ b/Documentation/guide.md
@@ -9,16 +9,18 @@ A guide to declaring, implementing, and using your own types with Objectively.
 
 Every Objectively type consists of three components:
 
-**1. The instance struct** — starts with the parent type, then the interface pointer, then instance variables:
+**1. The instance struct** — starts with the parent type, then the zero-length interface member, then instance variables:
 
 ```c
 struct Hello {
-    Object object;           // parent (starts-with = single inheritance)
-    HelloInterface *interface;
+    Object object;               // parent (starts-with = single inheritance)
+    HelloInterface *interface[0]; // carries a type, occupies no storage
     const char *greeting;
 };
 ```
 
+The `interface` member exists only so that `$` can read its type with `typeof`; it holds nothing. The interface itself lives on the Class and is reached through `Object::clazz`. The member MUST directly follow the parent, where its pointer alignment costs no padding.
+
 **2. The interface struct** — starts with the parent interface, then method function pointers:
 
 ```c
@@ -76,7 +78,6 @@ Class *_Hello(void) {
             .name            = "Hello",
             .superclass      = _Object(),
             .instanceSize    = sizeof(Hello),
-            .interfaceOffset = offsetof(Hello, interface),
             .interfaceSize   = sizeof(HelloInterface),
             .initialize      = initialize,
         });
@@ -139,6 +140,32 @@ To invoke a supertype's method implementation, use the `super` macro.
     super(Object, self, dealloc);
 ```
 
+## Re-classing an instance
+
+An instance carries no interface pointer of its own: `$`, `cast`, and `isKindOfClass` all resolve through `Object::clazz`. Reassigning `clazz` after allocation therefore changes an instance's behavior and its type identity together, immediately. This permits one-off Classes minted purely for behavior, with no struct, header, or archetype of their own:
+
+```c
+static void resizeHandle_captureEvent(Control *self, const SDL_Event *event) {
+    // ...
+}
+
+static void resizeHandle_initialize(Class *clazz) {
+    ((ControlInterface *) clazz->interface)->captureEvent = resizeHandle_captureEvent;
+}
+
+Class *proxy = _initialize(&(const ClassDef) {
+    .name          = "Control(resizeHandle)",
+    .superclass    = classof(resizeHandle),
+    .instanceSize  = classof(resizeHandle)->def.instanceSize,
+    .interfaceSize = classof(resizeHandle)->def.interfaceSize,
+    .initialize    = resizeHandle_initialize,
+});
+
+((Object *) resizeHandle)->clazz = proxy;
+```
+
+The new Class inherits every method of the original, since `_initialize` copies the superclass interface before calling `initialize`. The instance struct MUST NOT change: a Class minted this way SHOULD reuse the superclass's `instanceSize` exactly, because the memory has already been allocated.
+
 ## Managing memory
 
 Objectively uses reference counting to govern object retention. Newly instantiated Objects have a reference count of 1. To retain a strong reference to an Object, call `retain(obj)`. To relinquish it, call `release(obj)`. Once an Object's reference count reaches 0, it is deallocated. Remember to balance every `retain` with a `release`.
diff --git a/Examples/Hello.c b/Examples/Hello.c
index 5de79e0..940dd8b 100644
--- a/Examples/Hello.c
+++ b/Examples/Hello.c
@@ -82,7 +82,6 @@ Class *_Hello(void) {
       .name = "Hello",
       .superclass = _Object(),
       .instanceSize = sizeof(Hello),
-      .interfaceOffset = offsetof(Hello, interface),
       .interfaceSize = sizeof(HelloInterface),
       .initialize = initialize,
     });
diff --git a/Examples/Hello.h b/Examples/Hello.h
index c3222d7..0c67b10 100644
--- a/Examples/Hello.h
+++ b/Examples/Hello.h
@@ -37,9 +37,9 @@ struct Hello {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    */
-  HelloInterface *interface;
+  HelloInterface *interface[0];
 
   /**
    * @brief The greeting.
diff --git a/Sources/Objectively/Array.c b/Sources/Objectively/Array.c
index 73c719d..a407b7f 100644
--- a/Sources/Objectively/Array.c
+++ b/Sources/Objectively/Array.c
@@ -766,7 +766,6 @@ Class *_Array(void) {
       .name = "Array",
       .superclass = _Object(),
       .instanceSize = sizeof(Array),
-      .interfaceOffset = offsetof(Array, interface),
       .interfaceSize = sizeof(ArrayInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/Array.h b/Sources/Objectively/Array.h
index 3451369..5716810 100644
--- a/Sources/Objectively/Array.h
+++ b/Sources/Objectively/Array.h
@@ -61,10 +61,10 @@ struct Array {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  ArrayInterface *interface;
+  ArrayInterface *interface[0];
 
   /**
    * @brief The count of elements.
diff --git a/Sources/Objectively/Boole.c b/Sources/Objectively/Boole.c
index bc95eba..ded2d04 100644
--- a/Sources/Objectively/Boole.c
+++ b/Sources/Objectively/Boole.c
@@ -131,7 +131,6 @@ Class *_Boole(void) {
       .name = "Boole",
       .superclass = _Object(),
       .instanceSize = sizeof(Boole),
-      .interfaceOffset = offsetof(Boole, interface),
       .interfaceSize = sizeof(BooleInterface),
       .initialize = initialize,
       .destroy = destroy,
diff --git a/Sources/Objectively/Boole.h b/Sources/Objectively/Boole.h
index 18d5386..8fbfb07 100644
--- a/Sources/Objectively/Boole.h
+++ b/Sources/Objectively/Boole.h
@@ -46,10 +46,10 @@ struct Boole {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  BooleInterface *interface;
+  BooleInterface *interface[0];
 
   /**
    * @brief The backing bool.
diff --git a/Sources/Objectively/Class.c b/Sources/Objectively/Class.c
index bb8a8f9..d0a5e1b 100644
--- a/Sources/Objectively/Class.c
+++ b/Sources/Objectively/Class.c
@@ -157,7 +157,6 @@ Class *_initialize(const ClassDef *def) {
   assert(def->name);
   assert(def->instanceSize);
   assert(def->interfaceSize);
-  assert(def->interfaceOffset);
 
   Class *clazz = calloc(1, sizeof(Class));
   assert(clazz);
@@ -207,11 +206,6 @@ ident _alloc(Class *clazz) {
   object->clazz = clazz;
   object->referenceCount = 1;
 
-  ident interface = clazz->interface;
-  do {
-    *(ident *) (obj + clazz->def.interfaceOffset) = interface;
-  } while ((clazz = clazz->def.superclass));
-
   return obj;
 }
 
diff --git a/Sources/Objectively/Class.h b/Sources/Objectively/Class.h
index c900113..31eb62d 100644
--- a/Sources/Objectively/Class.h
+++ b/Sources/Objectively/Class.h
@@ -68,11 +68,6 @@ struct ClassDef {
    */
   size_t instanceSize;
 
-  /**
-   * @brief The interface offset (required).
-   */
-  ptrdiff_t interfaceOffset;
-
   /**
    * @brief The interface size (required).
    */
@@ -257,11 +252,22 @@ OBJECTIVELY_EXPORT size_t _pageSize;
 
 /**
  * @brief Invoke an instance method.
+ * @details The receiver's static type selects the interface layout: `typeof` of its
+ * zero-length `interface` member yields e.g. `StringInterface *` without that member
+ * occupying any storage. The interface itself is resolved through `Object::clazz`, so
+ * dispatch always follows the receiver's live Class, with every override in place.
+ * @remarks Instance dispatch, `isKindOfClass`, and `cast` all resolve through the same
+ * field, `Object::clazz`. There is no per-instance copy of the interface pointer. One
+ * consequence: reassigning `clazz` after allocation (Objective-C's `object_setClass`) is
+ * sound - type checks and dispatch see the new Class together, immediately. That makes
+ * runtime re-classing viable: proxies, spies, KVO-style observation, and Classes minted
+ * purely for behavior that reuse an existing struct's `instanceSize` with an overridden
+ * interface, without that struct declaring anything of its own (see issue #23).
  */
 #define $(obj, method, ...) \
   ({ \
-    typeof(obj) _obj = obj; \
-    _obj->interface->method(_obj, ## __VA_ARGS__); \
+    typeof(obj) _obj = (obj); \
+    ((typeof(_obj->interface[0])) classof(_obj)->interface)->method(_obj, ## __VA_ARGS__); \
   })
 
 /// @brief Invoke a Class method.
diff --git a/Sources/Objectively/Condition.c b/Sources/Objectively/Condition.c
index a5446ac..5aa8393 100644
--- a/Sources/Objectively/Condition.c
+++ b/Sources/Objectively/Condition.c
@@ -147,7 +147,6 @@ Class *_Condition(void) {
       .name = "Condition",
       .superclass = _Lock(),
       .instanceSize = sizeof(Condition),
-      .interfaceOffset = offsetof(Condition, interface),
       .interfaceSize = sizeof(ConditionInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/Condition.h b/Sources/Objectively/Condition.h
index ad4a134..06d1b69 100644
--- a/Sources/Objectively/Condition.h
+++ b/Sources/Objectively/Condition.h
@@ -49,10 +49,10 @@ struct Condition {
   Lock lock;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  ConditionInterface *interface;
+  ConditionInterface *interface[0];
 
   /**
    * @brief The backing condition.
diff --git a/Sources/Objectively/Data.c b/Sources/Objectively/Data.c
index 3fadfd0..d6d0aaa 100644
--- a/Sources/Objectively/Data.c
+++ b/Sources/Objectively/Data.c
@@ -425,7 +425,6 @@ Class *_Data(void) {
       .name = "Data",
       .superclass = _Object(),
       .instanceSize = sizeof(Data),
-      .interfaceOffset = offsetof(Data, interface),
       .interfaceSize = sizeof(DataInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/Data.h b/Sources/Objectively/Data.h
index bf0e787..123e27c 100644
--- a/Sources/Objectively/Data.h
+++ b/Sources/Objectively/Data.h
@@ -55,10 +55,10 @@ struct Data {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  DataInterface *interface;
+  DataInterface *interface[0];
 
   /**
    * @brief The bytes.
diff --git a/Sources/Objectively/Date.c b/Sources/Objectively/Date.c
index 4ae54fb..038f8d4 100644
--- a/Sources/Objectively/Date.c
+++ b/Sources/Objectively/Date.c
@@ -228,7 +228,6 @@ Class *_Date(void) {
       .name = "Date",
       .superclass = _Object(),
       .instanceSize = sizeof(Date),
-      .interfaceOffset = offsetof(Date, interface),
       .interfaceSize = sizeof(DateInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/Date.h b/Sources/Objectively/Date.h
index 1da7743..0c2dfa3 100644
--- a/Sources/Objectively/Date.h
+++ b/Sources/Objectively/Date.h
@@ -79,10 +79,10 @@ struct Date {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  DateInterface *interface;
+  DateInterface *interface[0];
 
   /**
    * @brief The time.
diff --git a/Sources/Objectively/DateFormatter.c b/Sources/Objectively/DateFormatter.c
index 719dc9b..0d917a8 100644
--- a/Sources/Objectively/DateFormatter.c
+++ b/Sources/Objectively/DateFormatter.c
@@ -138,7 +138,6 @@ Class *_DateFormatter(void) {
       .name = "DateFormatter",
       .superclass = _Object(),
       .instanceSize = sizeof(DateFormatter),
-      .interfaceOffset = offsetof(DateFormatter, interface),
       .interfaceSize = sizeof(DateFormatterInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/DateFormatter.h b/Sources/Objectively/DateFormatter.h
index e30557a..4961fda 100644
--- a/Sources/Objectively/DateFormatter.h
+++ b/Sources/Objectively/DateFormatter.h
@@ -58,10 +58,10 @@ struct DateFormatter {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  DateFormatterInterface *interface;
+  DateFormatterInterface *interface[0];
 
   /**
    * @brief The UTF-8 encoded format string.
diff --git a/Sources/Objectively/Dictionary.c b/Sources/Objectively/Dictionary.c
index 770895b..7c0bca4 100644
--- a/Sources/Objectively/Dictionary.c
+++ b/Sources/Objectively/Dictionary.c
@@ -768,7 +768,6 @@ Class *_Dictionary(void) {
       .name = "Dictionary",
       .superclass = _Object(),
       .instanceSize = sizeof(Dictionary),
-      .interfaceOffset = offsetof(Dictionary, interface),
       .interfaceSize = sizeof(DictionaryInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/Dictionary.h b/Sources/Objectively/Dictionary.h
index be35dc1..e7f3400 100644
--- a/Sources/Objectively/Dictionary.h
+++ b/Sources/Objectively/Dictionary.h
@@ -65,10 +65,10 @@ struct Dictionary {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  DictionaryInterface *interface;
+  DictionaryInterface *interface[0];
 
   /**
    * @brief The internal size (number of bins).
diff --git a/Sources/Objectively/Error.c b/Sources/Objectively/Error.c
index 26b239e..5ed0af2 100644
--- a/Sources/Objectively/Error.c
+++ b/Sources/Objectively/Error.c
@@ -172,7 +172,6 @@ Class *_Error(void) {
       .name = "Error",
       .superclass = _Object(),
       .instanceSize = sizeof(Error),
-      .interfaceOffset = offsetof(Error, interface),
       .interfaceSize = sizeof(ErrorInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/Error.h b/Sources/Objectively/Error.h
index 38d62e3..02d2c14 100644
--- a/Sources/Objectively/Error.h
+++ b/Sources/Objectively/Error.h
@@ -46,10 +46,10 @@ struct Error {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  ErrorInterface *interface;
+  ErrorInterface *interface[0];
 
   /**
    * @brief The error code.
diff --git a/Sources/Objectively/HashTable.c b/Sources/Objectively/HashTable.c
index bbceaf5..ead2222 100644
--- a/Sources/Objectively/HashTable.c
+++ b/Sources/Objectively/HashTable.c
@@ -334,7 +334,6 @@ Class *_HashTable(void) {
       .name = "HashTable",
       .superclass = _Object(),
       .instanceSize = sizeof(HashTable),
-      .interfaceOffset = offsetof(HashTable, interface),
       .interfaceSize = sizeof(HashTableInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/HashTable.h b/Sources/Objectively/HashTable.h
index b9fce74..8275f10 100644
--- a/Sources/Objectively/HashTable.h
+++ b/Sources/Objectively/HashTable.h
@@ -85,10 +85,10 @@ struct HashTable {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  HashTableInterface *interface;
+  HashTableInterface *interface[0];
 
   /**
    * @brief The number of entries.
diff --git a/Sources/Objectively/IndexPath.c b/Sources/Objectively/IndexPath.c
index 1a1c9bd..bd9f15e 100644
--- a/Sources/Objectively/IndexPath.c
+++ b/Sources/Objectively/IndexPath.c
@@ -186,7 +186,6 @@ Class *_IndexPath(void) {
       .name = "IndexPath",
       .superclass = _Object(),
       .instanceSize = sizeof(IndexPath),
-      .interfaceOffset = offsetof(IndexPath, interface),
       .interfaceSize = sizeof(IndexPathInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/IndexPath.h b/Sources/Objectively/IndexPath.h
index 42b23a5..6eaae05 100644
--- a/Sources/Objectively/IndexPath.h
+++ b/Sources/Objectively/IndexPath.h
@@ -45,10 +45,10 @@ struct IndexPath {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  IndexPathInterface *interface;
+  IndexPathInterface *interface[0];
 
   /**
    * @brief The indexes.
diff --git a/Sources/Objectively/IndexSet.c b/Sources/Objectively/IndexSet.c
index 555452d..2fec2ea 100644
--- a/Sources/Objectively/IndexSet.c
+++ b/Sources/Objectively/IndexSet.c
@@ -376,7 +376,6 @@ Class *_IndexSet(void) {
       .name = "IndexSet",
       .superclass = _Object(),
       .instanceSize = sizeof(IndexSet),
-      .interfaceOffset = offsetof(IndexSet, interface),
       .interfaceSize = sizeof(IndexSetInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/IndexSet.h b/Sources/Objectively/IndexSet.h
index 5decfe7..4ad2d75 100644
--- a/Sources/Objectively/IndexSet.h
+++ b/Sources/Objectively/IndexSet.h
@@ -46,10 +46,10 @@ struct IndexSet {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  IndexSetInterface *interface;
+  IndexSetInterface *interface[0];
 
   /**
    * @brief The indexes.
diff --git a/Sources/Objectively/JSONContext.c b/Sources/Objectively/JSONContext.c
index a5c194c..d9ef4ca 100644
--- a/Sources/Objectively/JSONContext.c
+++ b/Sources/Objectively/JSONContext.c
@@ -827,7 +827,6 @@ Class *_JSONContext(void) {
       .name = "JSONContext",
       .superclass = _Object(),
       .instanceSize = sizeof(JSONContext),
-      .interfaceOffset = offsetof(JSONContext, interface),
       .interfaceSize = sizeof(JSONContextInterface),
       .initialize = initialize,
       .destroy = destroy,
diff --git a/Sources/Objectively/JSONContext.h b/Sources/Objectively/JSONContext.h
index 27fd884..d1a6dd5 100644
--- a/Sources/Objectively/JSONContext.h
+++ b/Sources/Objectively/JSONContext.h
@@ -77,10 +77,10 @@ struct JSONContext {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  JSONContextInterface *interface;
+  JSONContextInterface *interface[0];
 
   /**
    * @brief Errors accumulated during the operation.
diff --git a/Sources/Objectively/JSONPath.c b/Sources/Objectively/JSONPath.c
index 585d0a9..4d028a8 100644
--- a/Sources/Objectively/JSONPath.c
+++ b/Sources/Objectively/JSONPath.c
@@ -124,7 +124,6 @@ Class *_JSONPath(void) {
       .name = "JSONPath",
       .superclass = _Object(),
       .instanceSize = sizeof(JSONPath),
-      .interfaceOffset = offsetof(JSONPath, interface),
       .interfaceSize = sizeof(JSONPathInterface),
       .initialize = initialize,
       .destroy = destroy,
diff --git a/Sources/Objectively/JSONPath.h b/Sources/Objectively/JSONPath.h
index 75b5895..9e90dfe 100644
--- a/Sources/Objectively/JSONPath.h
+++ b/Sources/Objectively/JSONPath.h
@@ -47,10 +47,10 @@ struct JSONPath {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  JSONPathInterface *interface;
+  JSONPathInterface *interface[0];
 };
 
 /**
diff --git a/Sources/Objectively/List.c b/Sources/Objectively/List.c
index 87743ef..4ad4897 100644
--- a/Sources/Objectively/List.c
+++ b/Sources/Objectively/List.c
@@ -412,7 +412,6 @@ Class *_List(void) {
       .name = "List",
       .superclass = _Object(),
       .instanceSize = sizeof(List),
-      .interfaceOffset = offsetof(List, interface),
       .interfaceSize = sizeof(ListInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/List.h b/Sources/Objectively/List.h
index f69319a..3c29390 100644
--- a/Sources/Objectively/List.h
+++ b/Sources/Objectively/List.h
@@ -65,10 +65,10 @@ struct List {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  ListInterface *interface;
+  ListInterface *interface[0];
 
   /**
    * @brief The number of elements.
diff --git a/Sources/Objectively/Lock.c b/Sources/Objectively/Lock.c
index 13991ea..e469deb 100644
--- a/Sources/Objectively/Lock.c
+++ b/Sources/Objectively/Lock.c
@@ -135,7 +135,6 @@ Class *_Lock(void) {
       .name = "Lock",
       .superclass = _Object(),
       .instanceSize = sizeof(Lock),
-      .interfaceOffset = offsetof(Lock, interface),
       .interfaceSize = sizeof(LockInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/Lock.h b/Sources/Objectively/Lock.h
index 8e3faa6..118781f 100644
--- a/Sources/Objectively/Lock.h
+++ b/Sources/Objectively/Lock.h
@@ -47,10 +47,10 @@ struct Lock {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  LockInterface *interface;
+  LockInterface *interface[0];
 
   /**
    * @brief The backing lock.
diff --git a/Sources/Objectively/Log.c b/Sources/Objectively/Log.c
index da9ec4c..402b09f 100644
--- a/Sources/Objectively/Log.c
+++ b/Sources/Objectively/Log.c
@@ -291,7 +291,6 @@ Class *_Log(void) {
       .name = "Log",
       .superclass = _Object(),
       .instanceSize = sizeof(Log),
-      .interfaceOffset = offsetof(Log, interface),
       .interfaceSize = sizeof(LogInterface),
       .initialize = initialize,
       .destroy = destroy,
diff --git a/Sources/Objectively/Log.h b/Sources/Objectively/Log.h
index c85aa14..78651c4 100644
--- a/Sources/Objectively/Log.h
+++ b/Sources/Objectively/Log.h
@@ -66,10 +66,10 @@ struct Log {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  LogInterface *interface;
+  LogInterface *interface[0];
 
   /**
    * @brief The format string, defaults to `LOG_FORMAT_DEFAULT`.
diff --git a/Sources/Objectively/Null.c b/Sources/Objectively/Null.c
index e1af58b..13ef45e 100644
--- a/Sources/Objectively/Null.c
+++ b/Sources/Objectively/Null.c
@@ -89,7 +89,6 @@ Class *_Null(void) {
       .name = "Null",
       .superclass = _Object(),
       .instanceSize = sizeof(Null),
-      .interfaceOffset = offsetof(Null, interface),
       .interfaceSize = sizeof(NullInterface),
       .initialize = initialize,
       .destroy = destroy,
diff --git a/Sources/Objectively/Null.h b/Sources/Objectively/Null.h
index 0593700..26de4d7 100644
--- a/Sources/Objectively/Null.h
+++ b/Sources/Objectively/Null.h
@@ -47,10 +47,10 @@ struct Null {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  NullInterface *interface;
+  NullInterface *interface[0];
 };
 
 /**
diff --git a/Sources/Objectively/Number.c b/Sources/Objectively/Number.c
index 6069940..83a2ce8 100644
--- a/Sources/Objectively/Number.c
+++ b/Sources/Objectively/Number.c
@@ -204,7 +204,6 @@ Class *_Number(void) {
       .name = "Number",
       .superclass = _Object(),
       .instanceSize = sizeof(Number),
-      .interfaceOffset = offsetof(Number, interface),
       .interfaceSize = sizeof(NumberInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/Number.h b/Sources/Objectively/Number.h
index 4f7fe75..7c63696 100644
--- a/Sources/Objectively/Number.h
+++ b/Sources/Objectively/Number.h
@@ -46,10 +46,10 @@ struct Number {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  NumberInterface *interface;
+  NumberInterface *interface[0];
 
   /**
    * @brief The backing value.
diff --git a/Sources/Objectively/NumberFormatter.c b/Sources/Objectively/NumberFormatter.c
index 260ef08..1648bb1 100644
--- a/Sources/Objectively/NumberFormatter.c
+++ b/Sources/Objectively/NumberFormatter.c
@@ -97,7 +97,6 @@ Class *_NumberFormatter(void) {
       .name = "NumberFormatter",
       .superclass = _Object(),
       .instanceSize = sizeof(NumberFormatter),
-      .interfaceOffset = offsetof(NumberFormatter, interface),
       .interfaceSize = sizeof(NumberFormatterInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/NumberFormatter.h b/Sources/Objectively/NumberFormatter.h
index c398619..db45afc 100644
--- a/Sources/Objectively/NumberFormatter.h
+++ b/Sources/Objectively/NumberFormatter.h
@@ -62,10 +62,10 @@ struct NumberFormatter {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  NumberFormatterInterface *interface;
+  NumberFormatterInterface *interface[0];
 
   /**
    * @brief The format string.
diff --git a/Sources/Objectively/Object.c b/Sources/Objectively/Object.c
index e84d7e6..fbd9c32 100644
--- a/Sources/Objectively/Object.c
+++ b/Sources/Objectively/Object.c
@@ -141,7 +141,6 @@ Class *_Object(void) {
     clazz = _initialize(&(const ClassDef) {
       .name = "Object",
       .instanceSize = sizeof(Object),
-      .interfaceOffset = offsetof(Object, interface),
       .interfaceSize = sizeof(ObjectInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/Object.h b/Sources/Objectively/Object.h
index f962386..dea0726 100644
--- a/Sources/Objectively/Object.h
+++ b/Sources/Objectively/Object.h
@@ -55,10 +55,10 @@ struct Object {
   Class *clazz;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  ObjectInterface *interface;
+  ObjectInterface *interface[0];
 
   /**
    * @brief The reference count of this Object.
diff --git a/Sources/Objectively/Operation.c b/Sources/Objectively/Operation.c
index a1f2e51..13eb17f 100644
--- a/Sources/Objectively/Operation.c
+++ b/Sources/Objectively/Operation.c
@@ -240,7 +240,6 @@ Class *_Operation(void) {
       .name = "Operation",
       .superclass = _Object(),
       .instanceSize = sizeof(Operation),
-      .interfaceOffset = offsetof(Operation, interface),
       .interfaceSize = sizeof(OperationInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/Operation.h b/Sources/Objectively/Operation.h
index 9b77b85..51d6b7d 100644
--- a/Sources/Objectively/Operation.h
+++ b/Sources/Objectively/Operation.h
@@ -58,10 +58,10 @@ struct Operation {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  OperationInterface *interface;
+  OperationInterface *interface[0];
 
   /**
    * @private
diff --git a/Sources/Objectively/OperationQueue.c b/Sources/Objectively/OperationQueue.c
index 37c7542..970231d 100644
--- a/Sources/Objectively/OperationQueue.c
+++ b/Sources/Objectively/OperationQueue.c
@@ -355,7 +355,6 @@ Class *_OperationQueue(void) {
       .name = "OperationQueue",
       .superclass = _Object(),
       .instanceSize = sizeof(OperationQueue),
-      .interfaceOffset = offsetof(OperationQueue, interface),
       .interfaceSize = sizeof(OperationQueueInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/OperationQueue.h b/Sources/Objectively/OperationQueue.h
index 77ecdab..47bdcd1 100644
--- a/Sources/Objectively/OperationQueue.h
+++ b/Sources/Objectively/OperationQueue.h
@@ -49,10 +49,10 @@ struct OperationQueue {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  OperationQueueInterface *interface;
+  OperationQueueInterface *interface[0];
 
   /**
    * @private
diff --git a/Sources/Objectively/Pointer.c b/Sources/Objectively/Pointer.c
index 66f7562..56f6dbf 100644
--- a/Sources/Objectively/Pointer.c
+++ b/Sources/Objectively/Pointer.c
@@ -143,7 +143,6 @@ Class *_Pointer(void) {
       .name = "Pointer",
       .superclass = _Object(),
       .instanceSize = sizeof(Pointer),
-      .interfaceOffset = offsetof(Pointer, interface),
       .interfaceSize = sizeof(PointerInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/Pointer.h b/Sources/Objectively/Pointer.h
index a2b57e3..22549c3 100644
--- a/Sources/Objectively/Pointer.h
+++ b/Sources/Objectively/Pointer.h
@@ -45,10 +45,10 @@ struct Pointer {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  PointerInterface *interface;
+  PointerInterface *interface[0];
 
   /**
    * @brief An optional destructor that, if set, is called on `dealloc`.
diff --git a/Sources/Objectively/PointerArray.c b/Sources/Objectively/PointerArray.c
index ac1b101..42d2cd2 100644
--- a/Sources/Objectively/PointerArray.c
+++ b/Sources/Objectively/PointerArray.c
@@ -187,7 +187,6 @@ Class *_PointerArray(void) {
       .name = "PointerArray",
       .superclass = _Object(),
       .instanceSize = sizeof(PointerArray),
-      .interfaceOffset = offsetof(PointerArray, interface),
       .interfaceSize = sizeof(PointerArrayInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/PointerArray.h b/Sources/Objectively/PointerArray.h
index 8362258..d85124e 100644
--- a/Sources/Objectively/PointerArray.h
+++ b/Sources/Objectively/PointerArray.h
@@ -49,10 +49,10 @@ struct PointerArray {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  PointerArrayInterface *interface;
+  PointerArrayInterface *interface[0];
 
   /**
    * @brief The capacity.
diff --git a/Sources/Objectively/RESTClient.c b/Sources/Objectively/RESTClient.c
index d4ae153..ce1f2c4 100644
--- a/Sources/Objectively/RESTClient.c
+++ b/Sources/Objectively/RESTClient.c
@@ -349,7 +349,6 @@ Class *_RESTClient(void) {
       .name = "RESTClient",
       .superclass = _Object(),
       .instanceSize = sizeof(RESTClient),
-      .interfaceOffset = offsetof(RESTClient, interface),
       .interfaceSize = sizeof(RESTClientInterface),
       .initialize = initialize,
       .destroy = destroy,
diff --git a/Sources/Objectively/RESTClient.h b/Sources/Objectively/RESTClient.h
index 448e25f..f445aa3 100644
--- a/Sources/Objectively/RESTClient.h
+++ b/Sources/Objectively/RESTClient.h
@@ -67,10 +67,10 @@ struct RESTClient {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  RESTClientInterface *interface;
+  RESTClientInterface *interface[0];
 
   /**
    * @brief The URLSession backing this client.
diff --git a/Sources/Objectively/Regexp.c b/Sources/Objectively/Regexp.c
index aa1bd40..05d5a4b 100644
--- a/Sources/Objectively/Regexp.c
+++ b/Sources/Objectively/Regexp.c
@@ -205,7 +205,6 @@ Class *_Regexp(void) {
       .name = "Regexp",
       .superclass = _Object(),
       .instanceSize = sizeof(Regexp),
-      .interfaceOffset = offsetof(Regexp, interface),
       .interfaceSize = sizeof(RegexpInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/Regexp.h b/Sources/Objectively/Regexp.h
index 2cd2f91..961fcc9 100644
--- a/Sources/Objectively/Regexp.h
+++ b/Sources/Objectively/Regexp.h
@@ -48,10 +48,10 @@ struct Regexp {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  RegexpInterface *interface;
+  RegexpInterface *interface[0];
 
   /**
    * @brief The pattern
diff --git a/Sources/Objectively/Resource.c b/Sources/Objectively/Resource.c
index 0f9eaeb..7958828 100644
--- a/Sources/Objectively/Resource.c
+++ b/Sources/Objectively/Resource.c
@@ -247,7 +247,6 @@ Class *_Resource(void) {
       .name = "Resource",
       .superclass = _Object(),
       .instanceSize = sizeof(Resource),
-      .interfaceOffset = offsetof(Resource, interface),
       .interfaceSize = sizeof(ResourceInterface),
       .initialize = initialize,
       .destroy = destroy,
diff --git a/Sources/Objectively/Resource.h b/Sources/Objectively/Resource.h
index dd4bc90..ac7c446 100644
--- a/Sources/Objectively/Resource.h
+++ b/Sources/Objectively/Resource.h
@@ -58,10 +58,10 @@ struct Resource {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  ResourceInterface *interface;
+  ResourceInterface *interface[0];
 
   /**
    * @brief The resource data.
diff --git a/Sources/Objectively/Set.c b/Sources/Objectively/Set.c
index 8223b20..945c618 100644
--- a/Sources/Objectively/Set.c
+++ b/Sources/Objectively/Set.c
@@ -675,7 +675,6 @@ Class *_Set(void) {
       .name = "Set",
       .superclass = _Object(),
       .instanceSize = sizeof(Set),
-      .interfaceOffset = offsetof(Set, interface),
       .interfaceSize = sizeof(SetInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/Set.h b/Sources/Objectively/Set.h
index d1161cb..30e5d3e 100644
--- a/Sources/Objectively/Set.h
+++ b/Sources/Objectively/Set.h
@@ -60,10 +60,10 @@ struct Set {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  SetInterface *interface;
+  SetInterface *interface[0];
 
   /**
    * @brief The internal size (number of bins).
diff --git a/Sources/Objectively/String.c b/Sources/Objectively/String.c
index 93e84f9..90e8368 100644
--- a/Sources/Objectively/String.c
+++ b/Sources/Objectively/String.c
@@ -1005,7 +1005,6 @@ Class *_String(void) {
       .name = "String",
       .superclass = _Object(),
       .instanceSize = sizeof(String),
-      .interfaceOffset = offsetof(String, interface),
       .interfaceSize = sizeof(StringInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/String.h b/Sources/Objectively/String.h
index edffeba..de33986 100644
--- a/Sources/Objectively/String.h
+++ b/Sources/Objectively/String.h
@@ -74,10 +74,10 @@ struct String {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  StringInterface *interface;
+  StringInterface *interface[0];
 
   /**
    * @brief The backing null-terminated UTF-8 encoded character array.
diff --git a/Sources/Objectively/StringReader.c b/Sources/Objectively/StringReader.c
index 266a6e5..bc8be98 100644
--- a/Sources/Objectively/StringReader.c
+++ b/Sources/Objectively/StringReader.c
@@ -198,7 +198,6 @@ Class *_StringReader(void) {
       .name = "StringReader",
       .superclass = _Object(),
       .instanceSize = sizeof(StringReader),
-      .interfaceOffset = offsetof(StringReader, interface),
       .interfaceSize = sizeof(StringReaderInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/StringReader.h b/Sources/Objectively/StringReader.h
index 34761ea..ab13090 100644
--- a/Sources/Objectively/StringReader.h
+++ b/Sources/Objectively/StringReader.h
@@ -52,10 +52,10 @@ struct StringReader {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  StringReaderInterface *interface;
+  StringReaderInterface *interface[0];
 
   /**
    * @brief The StringReader head.
diff --git a/Sources/Objectively/Thread.c b/Sources/Objectively/Thread.c
index c7bcce4..02c282c 100644
--- a/Sources/Objectively/Thread.c
+++ b/Sources/Objectively/Thread.c
@@ -212,7 +212,6 @@ Class *_Thread(void) {
       .name = "Thread",
       .superclass = _Object(),
       .instanceSize = sizeof(Thread),
-      .interfaceOffset = offsetof(Thread, interface),
       .interfaceSize = sizeof(ThreadInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/Thread.h b/Sources/Objectively/Thread.h
index 4a6f0d0..8a3e341 100644
--- a/Sources/Objectively/Thread.h
+++ b/Sources/Objectively/Thread.h
@@ -58,10 +58,10 @@ struct Thread {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  ThreadInterface *interface;
+  ThreadInterface *interface[0];
 
   /**
    * @brief The user data.
diff --git a/Sources/Objectively/URL.c b/Sources/Objectively/URL.c
index 28f7dae..0b327f8 100644
--- a/Sources/Objectively/URL.c
+++ b/Sources/Objectively/URL.c
@@ -254,7 +254,6 @@ Class *_URL(void) {
       .name = "URL",
       .superclass = _Object(),
       .instanceSize = sizeof(URL),
-      .interfaceOffset = offsetof(URL, interface),
       .interfaceSize = sizeof(URLInterface),
       .initialize = initialize,
       .destroy = destroy,
diff --git a/Sources/Objectively/URL.h b/Sources/Objectively/URL.h
index 3f3fbe7..01c91c5 100644
--- a/Sources/Objectively/URL.h
+++ b/Sources/Objectively/URL.h
@@ -49,10 +49,10 @@ struct URL {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  URLInterface *interface;
+  URLInterface *interface[0];
 
   /**
    * @brief The fragment.
diff --git a/Sources/Objectively/URLCache.c b/Sources/Objectively/URLCache.c
index 7e8e0b8..ff048df 100644
--- a/Sources/Objectively/URLCache.c
+++ b/Sources/Objectively/URLCache.c
@@ -417,7 +417,6 @@ Class *_URLCache(void) {
       .name = "URLCache",
       .superclass = _Object(),
       .instanceSize = sizeof(URLCache),
-      .interfaceOffset = offsetof(URLCache, interface),
       .interfaceSize = sizeof(URLCacheInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/URLCache.h b/Sources/Objectively/URLCache.h
index 2dec83c..d7baa0e 100644
--- a/Sources/Objectively/URLCache.h
+++ b/Sources/Objectively/URLCache.h
@@ -49,10 +49,10 @@ struct URLCache {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  URLCacheInterface *interface;
+  URLCacheInterface *interface[0];
 
   /**
    * @brief The lock protecting this cache.
diff --git a/Sources/Objectively/URLCachedResponse.c b/Sources/Objectively/URLCachedResponse.c
index 74a2fb4..d6743e9 100644
--- a/Sources/Objectively/URLCachedResponse.c
+++ b/Sources/Objectively/URLCachedResponse.c
@@ -170,7 +170,6 @@ Class *_URLCachedResponse(void) {
       .name = "URLCachedResponse",
       .superclass = _Object(),
       .instanceSize = sizeof(URLCachedResponse),
-      .interfaceOffset = offsetof(URLCachedResponse, interface),
       .interfaceSize = sizeof(URLCachedResponseInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/URLCachedResponse.h b/Sources/Objectively/URLCachedResponse.h
index 1a74880..18d1435 100644
--- a/Sources/Objectively/URLCachedResponse.h
+++ b/Sources/Objectively/URLCachedResponse.h
@@ -49,10 +49,10 @@ struct URLCachedResponse {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  URLCachedResponseInterface *interface;
+  URLCachedResponseInterface *interface[0];
 
   /**
    * @brief The HTTP response.
diff --git a/Sources/Objectively/URLRequest.c b/Sources/Objectively/URLRequest.c
index 50880aa..fe230b5 100644
--- a/Sources/Objectively/URLRequest.c
+++ b/Sources/Objectively/URLRequest.c
@@ -210,7 +210,6 @@ Class *_URLRequest(void) {
       .name = "URLRequest",
       .superclass = _Object(),
       .instanceSize = sizeof(URLRequest),
-      .interfaceOffset = offsetof(URLRequest, interface),
       .interfaceSize = sizeof(URLRequestInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/URLRequest.h b/Sources/Objectively/URLRequest.h
index 831b08a..5f54c5b 100644
--- a/Sources/Objectively/URLRequest.h
+++ b/Sources/Objectively/URLRequest.h
@@ -63,10 +63,10 @@ struct URLRequest {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  URLRequestInterface *interface;
+  URLRequestInterface *interface[0];
 
   /**
    * @brief The HTTP request body, sent as `POST` or `PUT` data.
diff --git a/Sources/Objectively/URLResponse.c b/Sources/Objectively/URLResponse.c
index 55cb862..8b93120 100644
--- a/Sources/Objectively/URLResponse.c
+++ b/Sources/Objectively/URLResponse.c
@@ -117,7 +117,6 @@ Class *_URLResponse(void) {
       .name = "URLResponse",
       .superclass = _Object(),
       .instanceSize = sizeof(URLResponse),
-      .interfaceOffset = offsetof(URLResponse, interface),
       .interfaceSize = sizeof(URLResponseInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/URLResponse.h b/Sources/Objectively/URLResponse.h
index 128af43..db154fd 100644
--- a/Sources/Objectively/URLResponse.h
+++ b/Sources/Objectively/URLResponse.h
@@ -47,10 +47,10 @@ struct URLResponse {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  URLResponseInterface *interface;
+  URLResponseInterface *interface[0];
 
   /**
    * @brief The HTTP response headers.
diff --git a/Sources/Objectively/URLSession.c b/Sources/Objectively/URLSession.c
index 3f097a6..f24b1d2 100644
--- a/Sources/Objectively/URLSession.c
+++ b/Sources/Objectively/URLSession.c
@@ -420,7 +420,6 @@ Class *_URLSession(void) {
       .name = "URLSession",
       .superclass = _Object(),
       .instanceSize = sizeof(URLSession),
-      .interfaceOffset = offsetof(URLSession, interface),
       .interfaceSize = sizeof(URLSessionInterface),
       .initialize = initialize,
       .destroy = destroy,
diff --git a/Sources/Objectively/URLSession.h b/Sources/Objectively/URLSession.h
index ed42281..b0304a6 100644
--- a/Sources/Objectively/URLSession.h
+++ b/Sources/Objectively/URLSession.h
@@ -62,10 +62,10 @@ struct URLSession {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  URLSessionInterface *interface;
+  URLSessionInterface *interface[0];
 
   /**
    * @private
diff --git a/Sources/Objectively/URLSessionConfiguration.c b/Sources/Objectively/URLSessionConfiguration.c
index 168597d..2f2adda 100644
--- a/Sources/Objectively/URLSessionConfiguration.c
+++ b/Sources/Objectively/URLSessionConfiguration.c
@@ -68,7 +68,6 @@ Class *_URLSessionConfiguration(void) {
       .name = "URLSessionConfiguration",
       .superclass = _Object(),
       .instanceSize = sizeof(URLSessionConfiguration),
-      .interfaceOffset = offsetof(URLSessionConfiguration, interface),
       .interfaceSize = sizeof(URLSessionConfigurationInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/URLSessionConfiguration.h b/Sources/Objectively/URLSessionConfiguration.h
index 987cb63..d5397a6 100644
--- a/Sources/Objectively/URLSessionConfiguration.h
+++ b/Sources/Objectively/URLSessionConfiguration.h
@@ -49,10 +49,10 @@ struct URLSessionConfiguration {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  URLSessionConfigurationInterface *interface;
+  URLSessionConfigurationInterface *interface[0];
 
   /**
    * @brief Credentials for URLRequests requiring authentication.
diff --git a/Sources/Objectively/URLSessionDataTask.c b/Sources/Objectively/URLSessionDataTask.c
index 2fd36eb..5a0a81d 100644
--- a/Sources/Objectively/URLSessionDataTask.c
+++ b/Sources/Objectively/URLSessionDataTask.c
@@ -234,7 +234,6 @@ Class *_URLSessionDataTask(void) {
       .name = "URLSessionDataTask",
       .superclass = _URLSessionTask(),
       .instanceSize = sizeof(URLSessionDataTask),
-      .interfaceOffset = offsetof(URLSessionDataTask, interface),
       .interfaceSize = sizeof(URLSessionDataTaskInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/URLSessionDataTask.h b/Sources/Objectively/URLSessionDataTask.h
index 30c83f4..2ae2bed 100644
--- a/Sources/Objectively/URLSessionDataTask.h
+++ b/Sources/Objectively/URLSessionDataTask.h
@@ -49,10 +49,10 @@ struct URLSessionDataTask {
   URLSessionTask urlSessionTask;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  URLSessionDataTaskInterface *interface;
+  URLSessionDataTaskInterface *interface[0];
 
   /**
    * @brief The data received.
diff --git a/Sources/Objectively/URLSessionDownloadTask.c b/Sources/Objectively/URLSessionDownloadTask.c
index 1fda97b..0e4e153 100644
--- a/Sources/Objectively/URLSessionDownloadTask.c
+++ b/Sources/Objectively/URLSessionDownloadTask.c
@@ -83,7 +83,6 @@ Class *_URLSessionDownloadTask(void) {
       .name = "URLSessionDownloadTask",
       .superclass = _URLSessionTask(),
       .instanceSize = sizeof(URLSessionDownloadTask),
-      .interfaceOffset = offsetof(URLSessionDownloadTask, interface),
       .interfaceSize = sizeof(URLSessionDownloadTaskInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/URLSessionDownloadTask.h b/Sources/Objectively/URLSessionDownloadTask.h
index fcfc239..32afc21 100644
--- a/Sources/Objectively/URLSessionDownloadTask.h
+++ b/Sources/Objectively/URLSessionDownloadTask.h
@@ -48,10 +48,10 @@ struct URLSessionDownloadTask {
   URLSessionTask urlSessionTask;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  URLSessionDownloadTaskInterface *interface;
+  URLSessionDownloadTaskInterface *interface[0];
 
   /**
    * @brief The target FILE.
diff --git a/Sources/Objectively/URLSessionTask.c b/Sources/Objectively/URLSessionTask.c
index 66850fb..3c1c038 100644
--- a/Sources/Objectively/URLSessionTask.c
+++ b/Sources/Objectively/URLSessionTask.c
@@ -348,7 +348,6 @@ Class *_URLSessionTask(void) {
       .name = "URLSessionTask",
       .superclass = _Object(),
       .instanceSize = sizeof(URLSessionTask),
-      .interfaceOffset = offsetof(URLSessionTask, interface),
       .interfaceSize = sizeof(URLSessionTaskInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/URLSessionTask.h b/Sources/Objectively/URLSessionTask.h
index 963ffac..33091ad 100644
--- a/Sources/Objectively/URLSessionTask.h
+++ b/Sources/Objectively/URLSessionTask.h
@@ -73,10 +73,10 @@ struct URLSessionTask {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  URLSessionTaskInterface *interface;
+  URLSessionTaskInterface *interface[0];
 
   /**
    * @private
diff --git a/Sources/Objectively/URLSessionUploadTask.c b/Sources/Objectively/URLSessionUploadTask.c
index dab609c..b36c7d9 100644
--- a/Sources/Objectively/URLSessionUploadTask.c
+++ b/Sources/Objectively/URLSessionUploadTask.c
@@ -93,7 +93,6 @@ Class *_URLSessionUploadTask(void) {
       .name = "URLSessionUploadTask",
       .superclass = _URLSessionTask(),
       .instanceSize = sizeof(URLSessionUploadTask),
-      .interfaceOffset = offsetof(URLSessionUploadTask, interface),
       .interfaceSize = sizeof(URLSessionUploadTaskInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/URLSessionUploadTask.h b/Sources/Objectively/URLSessionUploadTask.h
index 5ba0b3b..8c703cf 100644
--- a/Sources/Objectively/URLSessionUploadTask.h
+++ b/Sources/Objectively/URLSessionUploadTask.h
@@ -48,10 +48,10 @@ struct URLSessionUploadTask {
   URLSessionTask urlSessionTask;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  URLSessionUploadTaskInterface *interface;
+  URLSessionUploadTaskInterface *interface[0];
 
   /**
    * @brief The FILE to upload.
diff --git a/Sources/Objectively/Vector.c b/Sources/Objectively/Vector.c
index 4b48fbc..85db78d 100644
--- a/Sources/Objectively/Vector.c
+++ b/Sources/Objectively/Vector.c
@@ -456,7 +456,6 @@ Class *_Vector(void) {
       .name = "Vector",
       .superclass = _Object(),
       .instanceSize = sizeof(Vector),
-      .interfaceOffset = offsetof(Vector, interface),
       .interfaceSize = sizeof(VectorInterface),
       .initialize = initialize,
     });
diff --git a/Sources/Objectively/Vector.h b/Sources/Objectively/Vector.h
index 1cce9c6..6d17189 100644
--- a/Sources/Objectively/Vector.h
+++ b/Sources/Objectively/Vector.h
@@ -56,10 +56,10 @@ struct Vector {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  VectorInterface *interface;
+  VectorInterface *interface[0];
 
   /**
    * @brief The capacity.
diff --git a/Templates/Eclipse/eclipse-code-templates.xml b/Templates/Eclipse/eclipse-code-templates.xml
index 821078f..e29821e 100644
--- a/Templates/Eclipse/eclipse-code-templates.xml
+++ b/Templates/Eclipse/eclipse-code-templates.xml
@@ -64,7 +64,6 @@ Class *_${file_base}(void) {
       .name = "${file_base}",
       .superclass = _Object(),
       .instanceSize = sizeof(${file_base}),
-      .interfaceOffset = offsetof(${file_base}, interface),
       .interfaceSize = sizeof(${file_base}Interface),
       .initialize = initialize,
     });
@@ -100,10 +99,10 @@ struct ${file_base} {
   Object object;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  ${file_base}Interface *interface;
+  ${file_base}Interface *interface[0];
 
   //.. 
 };
diff --git a/Templates/Xcode/Objectively C Type.xctemplate/___FILEBASENAME___.c b/Templates/Xcode/Objectively C Type.xctemplate/___FILEBASENAME___.c
index 4d2a8e4..fb88be8 100644
--- a/Templates/Xcode/Objectively C Type.xctemplate/___FILEBASENAME___.c	
+++ b/Templates/Xcode/Objectively C Type.xctemplate/___FILEBASENAME___.c	
@@ -70,7 +70,6 @@ Class *____FILEBASENAMEASIDENTIFIER___(void) {
       .name = "___FILEBASENAMEASIDENTIFIER___",
       .superclass = ____VARIABLE_superclass:identifier___(),
       .instanceSize = sizeof(___FILEBASENAMEASIDENTIFIER___),
-      .interfaceOffset = offsetof(___FILEBASENAMEASIDENTIFIER___, interface),
       .interfaceSize = sizeof(___FILEBASENAMEASIDENTIFIER___Interface),
       .initialize = initialize,
     });
diff --git a/Templates/Xcode/Objectively C Type.xctemplate/___FILEBASENAME___.h b/Templates/Xcode/Objectively C Type.xctemplate/___FILEBASENAME___.h
index e372743..1dc304b 100644
--- a/Templates/Xcode/Objectively C Type.xctemplate/___FILEBASENAME___.h	
+++ b/Templates/Xcode/Objectively C Type.xctemplate/___FILEBASENAME___.h	
@@ -30,10 +30,10 @@ struct ___FILEBASENAMEASIDENTIFIER___ {
   ___VARIABLE_superclass:identifier___ ___VARIABLE_superclassMember:identifier___;
 
   /**
-   * @brief The interface.
+   * @brief The interface type.
    * @protected
    */
-  ___FILEBASENAMEASIDENTIFIER___Interface *interface;
+  ___FILEBASENAMEASIDENTIFIER___Interface *interface[0];
 
   //..
 };

From 097090fd91437f0a1ceb730c8fec776c4f53a815 Mon Sep 17 00:00:00 2001
From: Jay Dolan <jay@jaydolan.com>
Date: Wed, 2 Sep 2026 19:25:45 -0400
Subject: [PATCH 2/5] Doc fix.

---
 Documentation/guide.md | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Documentation/guide.md b/Documentation/guide.md
index 50e8b0b..ec32815 100644
--- a/Documentation/guide.md
+++ b/Documentation/guide.md
@@ -145,8 +145,9 @@ To invoke a supertype's method implementation, use the `super` macro.
 An instance carries no interface pointer of its own: `$`, `cast`, and `isKindOfClass` all resolve through `Object::clazz`. Reassigning `clazz` after allocation therefore changes an instance's behavior and its type identity together, immediately. This permits one-off Classes minted purely for behavior, with no struct, header, or archetype of their own:
 
 ```c
-static void resizeHandle_captureEvent(Control *self, const SDL_Event *event) {
+static bool resizeHandle_captureEvent(Control *self, const SDL_Event *event) {
     // ...
+    return true;
 }
 
 static void resizeHandle_initialize(Class *clazz) {

From 694ef457669b118b5132f797f8f14d3a6284c395 Mon Sep 17 00:00:00 2001
From: Jay Dolan <jay@jaydolan.com>
Date: Wed, 2 Sep 2026 19:26:42 -0400
Subject: [PATCH 3/5] Add regression test for re-classing an instance

Dispatch and type identity both resolve through Object::clazz, so reassigning it
must change what `$` calls immediately while the instance remains a kind of its
original Class. Mint a Class from classof(object) at runtime, swap clazz, and
assert both, then swap back. Guards against reintroducing a per-instance
interface pointer.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
---
 Tests/Objectively/Object.c | 49 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/Tests/Objectively/Object.c b/Tests/Objectively/Object.c
index c520208..69307d7 100644
--- a/Tests/Objectively/Object.c
+++ b/Tests/Objectively/Object.c
@@ -55,10 +55,59 @@ START_TEST(object) {
 
 } END_TEST
 
+static int reclassedHash(const Object *self) {
+  return 0x5eed;
+}
+
+static void reclassInitialize(Class *clazz) {
+  ((ObjectInterface *) clazz->interface)->hash = reclassedHash;
+}
+
+/*
+ * Dispatch and type identity both resolve through Object::clazz, so reassigning it
+ * must change what `$` calls immediately, while the instance remains a kind of its
+ * original Class. Guards against reintroducing a per-instance interface pointer.
+ */
+START_TEST(reclass) {
+
+  Object *object = $(alloc(Object), init);
+  ck_assert_ptr_ne(NULL, object);
+
+  const int hash = $(object, hash);
+  ck_assert_int_ne(0x5eed, hash);
+
+  Class *proxy = _initialize(&(const ClassDef) {
+    .name = "Object(reclass)",
+    .superclass = classof(object),
+    .instanceSize = classof(object)->def.instanceSize,
+    .interfaceSize = classof(object)->def.interfaceSize,
+    .initialize = reclassInitialize,
+  });
+
+  object->clazz = proxy;
+
+  ck_assert_ptr_eq(proxy, classof(object));
+  ck_assert_int_eq(0x5eed, $(object, hash));
+
+  ck_assert($(object, isKindOfClass, proxy));
+  ck_assert($(object, isKindOfClass, _Object()));
+  ck_assert(instanceof(Object, object));
+
+  ck_assert($(object, isEqual, object));
+
+  object->clazz = _Object();
+
+  ck_assert_int_eq(hash, $(object, hash));
+
+  release(object);
+
+} END_TEST
+
 int main(int argc, char **argv) {
 
   TCase *tcase = tcase_create("Object");
   tcase_add_test(tcase, object);
+  tcase_add_test(tcase, reclass);
 
   Suite *suite = suite_create("Object");
   suite_add_tcase(suite, tcase);

From 791d71e249492c8039a8c6a216e879297c25e814 Mon Sep 17 00:00:00 2001
From: Jay Dolan <jay@jaydolan.com>
Date: Wed, 2 Sep 2026 19:32:36 -0400
Subject: [PATCH 4/5] Bump version to 2.2.0

Instance layout changed: the per-instance interface pointers are gone, so
sizeof every type shrinks. Downstream libraries MUST be rebuilt against this
release; ObjectivelyGPU and ObjectivelyMVC require >= 2.2.0.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
---
 configure.ac | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/configure.ac b/configure.ac
index b58a42f..4ea3904 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1,6 +1,6 @@
 AC_PREREQ(2.69)
 
-AC_INIT([Objectively], [2.0.23], [jay@jaydolan.com])
+AC_INIT([Objectively], [2.2.0], [jay@jaydolan.com])
 
 AC_CONFIG_HEADERS([Sources/Objectively/Config.h])
 AC_CONFIG_MACRO_DIR([m4])

From 80b6c7575aa32f6bdeaf3493461793a57bc8d9c7 Mon Sep 17 00:00:00 2001
From: Jay Dolan <jay@jaydolan.com>
Date: Wed, 2 Sep 2026 19:38:55 -0400
Subject: [PATCH 5/5] Derive the shared library soname from the package version

Replace hand-maintained libtool -version-info with -release MAJOR.MINOR, computed
from AC_INIT. Every minor release gets a new soname, so a binary built against an
older release fails to load rather than reading changed struct layouts; patch
releases stay compatible. Nothing outside these repositories links Objectively,
so there is no separately shipped consumer for current:revision:age to serve.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
---
 Sources/Objectively/Makefile.am | 2 +-
 configure.ac                    | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/Sources/Objectively/Makefile.am b/Sources/Objectively/Makefile.am
index 3b50d3a..bf57931 100644
--- a/Sources/Objectively/Makefile.am
+++ b/Sources/Objectively/Makefile.am
@@ -117,7 +117,7 @@ libObjectively_la_CFLAGS = \
 
 libObjectively_la_LDFLAGS = \
 	@HOST_LDFLAGS@ \
-	-version-info @LT_VERSION@
+	-release @RELEASE_VERSION@
 
 libObjectively_la_LIBADD = \
 	-lpthread \
diff --git a/configure.ac b/configure.ac
index 4ea3904..1b432b8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -13,7 +13,7 @@ AC_USE_SYSTEM_EXTENSIONS
 AC_PROG_CC
 AC_PROG_CXX
 LT_INIT
-AC_SUBST([LT_VERSION], [2:0:0])
+AC_SUBST([RELEASE_VERSION], [m4_bpatsubst(AC_PACKAGE_VERSION, [\.[0-9]*$], [])])
 
 AM_INIT_AUTOMAKE([foreign])
 AM_SILENT_RULES([yes])