实现了多态，但是只能单继承，且父类必须放在子类最开头。

main.c

@@ -6,7 +6,10 @@
 #include <assert.h>
 
 #define VIRTUAL  
-#define PRIVATE  
+#define PRIVATE static 
+
+#define ASSERT_CALL_VIRTUAL_METHOD() assert(!("can't call abstract method"))
+
 
 struct _virtual_table
 {
@@ -16,42 +19,51 @@ struct _virtual_table
 
 void virtual_area(void *self)
 {
-    assert(!"can't call abstract method");
+    ASSERT_CALL_VIRTUAL_METHOD();
 }
 
 void virtual_draw(void *self)
 {
-    assert(!"can't call abstract method");
+    ASSERT_CALL_VIRTUAL_METHOD();
 }
 
 struct _virtual_table *virtual_new(void)
 {
-    struct _virtual_table *v = calloc(1, sizeof(struct _virtual_table));
-    if (v == NULL)
+    struct _virtual_table *vtb = calloc(1, sizeof(struct _virtual_table));
+    if (vtb == NULL)
     {
         return NULL;
     }
-    v->area = virtual_area;
-    v->draw = virtual_draw;
-    return v;
+    vtb->area = virtual_area;
+    vtb->draw = virtual_draw;
+    return vtb;
 }
 
-
-
 struct _shape
 {
-    VIRTUAL void (*area)(void *self);
-    VIRTUAL void (*draw)(void *self);
+    struct _virtual_table *vtb;
 };
 
 void shape_area(void *self)
 {
-    assert(!"can't call abstract method");
+    struct _shape *this = (struct _shape *)self;
+    this->vtb->area(self);
 }
 
 void shape_draw(void *self)
 {
-    assert(!"can't call abstract method");
+    struct _shape *this = (struct _shape *)self;
+    this->vtb->draw(self);
+}
+
+PRIVATE void _shape_area(void *self)
+{
+    ASSERT_CALL_VIRTUAL_METHOD();
+}
+
+PRIVATE void _shape_draw(void *self)
+{
+    ASSERT_CALL_VIRTUAL_METHOD();
 }
 
 struct _shape *shape_new(void)
@@ -61,11 +73,16 @@ struct _shape *shape_new(void)
     {
         return NULL;
     }
-    shape->area = shape_area;
-    shape->draw = shape_draw;
+    static struct _virtual_table vtb = {
+        .area = (void (*)(void *self))_shape_area, 
+        .draw = (void (*)(void *self))_shape_draw
+    };
+    shape->vtb = &vtb;
     return shape;
 }
 
+#define SUPER(self) (&(self)->shape)
+
 #if 0
 void shape_free(struct _shape * self)
 {
@@ -76,12 +93,10 @@ void shape_free(struct _shape * self)
 }
 #endif
 
-#define SUPER(self) ((self)->shape)
-
 struct _rect
 {
     // super
-    struct _shape* shape;
+    struct _shape shape;
 
     // attribute
     double width, height;
@@ -111,21 +126,19 @@ struct _rect *rect_new(double width, double height)
     rect->width = width;
     rect->height = height;
 
-    rect->shape = shape_new();
-    if (rect->shape == NULL)
-    {
-        return NULL;
-    }
+    static struct _virtual_table vtb = {
+        .area = (void (*)(void *self))rect_area,
+        .draw = (void (*)(void *self))rect_draw
+    };
 
-    SUPER(rect)->area = (void (*)(void *self))rect_area;
-    SUPER(rect)->draw = (void (*)(void *self))rect_draw;
+    SUPER(rect)->vtb = &vtb;
     return rect;
 }
 
 struct _circle
 {
     // super
-    struct _shape *shape;
+    struct _shape shape;
 
     // attribute
     double radius;
@@ -151,16 +164,14 @@ struct _circle *circle_new(double radius)
     {
         return NULL;
     }
-    circle->shape = shape_new();
-    if (circle->shape == NULL)
-    {
-        return NULL;
-    }
-
     circle->radius = radius;
 
-    SUPER(circle)->area = (void (*)(void *self))circle_area;
-    SUPER(circle)->draw = (void (*)(void *self))circle_draw;
+    static struct _virtual_table vtb = {
+        .area = (void (*)(void *self))circle_area,
+        .draw = (void (*)(void *self))circle_draw,
+    };
+
+    SUPER(circle)->vtb = &vtb;
     return circle;
 }
 
@@ -174,15 +185,28 @@ int main(int argc, char *argv[])
     circle_area(circle);
     circle_draw(circle);
 
-    // struct shape *shape = shape_new();
-    // shape_area(shape);
-    // shape_draw(shape);
+    printf("------------------------------\n");
+    shape_area(rect);
+    shape_area(circle);
 
-    // struct _shape *shape = NULL;
-    struct _shape *shape = rect_new(2,3);
-    // shape = rect;
+    shape_draw(rect);
+    shape_draw(circle);
+
+    printf("------------------------------\n");
+    struct _shape *shape = (struct _shape *)rect_new(2,3);
     shape_area(shape);
     shape_draw(shape);
 
+    struct _shape *shape2 = NULL;
+    shape2 = (struct _shape *)circle;
+    shape_area(shape2);
+    shape_draw(shape2);
+
+
+    printf("------------------------------\n");
+    struct _shape *shape3 = shape_new();
+    shape_area(shape3);
+    shape_draw(shape3);
+
     return 0;
 }