Methods and Primitives are now identified by is_invokable()

Using a mixing as introduced in b159370a is not sufficient.
We want to be able to know whether an object is Method/Primitive and using the type test as with multiple inheritance does not work anymore.
Signed-off-by: Stefan Marr <git@stefan-marr.de>

src/som/vmobjects/invokable.py

-# An 'interface', or common super class for methods and primitives. 
 class Invokable(object):
-
-    _mixin_ = True
+    """An 'interface', or common super class for methods and primitives.
+       WARNING: This interface is not used in the RPython version, because
+                RPython does not support multiple inheritance.
+                It is kept merely for informative purposes to show the common
+                parts of Method and Primitive.
+    """
 
     # Tells whether this is a primitive
     def is_primitive(self):

src/som/vmobjects/method.py

 from __future__ import absolute_import
 
-from som.vmobjects.array     import Array
-from som.vmobjects.invokable import Invokable
+from som.vmobjects.array import Array
 
-from som.interpreter.bytecodes import Bytecodes
+from som.interpreter.bytecodes import bytecode_length
 
 from array import array
 
-class Method(Array, Invokable):
+class Method(Array):
     
     # Static field indices and number of method fields
     NUMBER_OF_LOCALS_INDEX                 = 1 + Array.CLASS_INDEX
@@ -32,6 +31,12 @@ class Method(Array, Invokable):
     
     def is_primitive(self):
         return False
+    
+    def is_invokable(self):
+        """In the RPython version, we use this method to identify methods 
+           and primitives
+        """
+        return True
   
     def get_number_of_locals(self):
         # Get the number of locals (converted to a Java integer)
@@ -69,7 +74,7 @@ class Method(Array, Invokable):
 
         # Make sure all nested invokables have the same holder
         for i in range(0, self.get_number_of_indexable_fields()):
-            if isinstance(self.get_indexable_field(i), Invokable):
+            if self.get_indexable_field(i).is_invokable():
                 self.get_indexable_field(i).set_holder(value)
 
     def get_constant(self, bytecode_index):
@@ -125,7 +130,7 @@ class Method(Array, Invokable):
         i = 0
         while i < len(self._bytecodes):
             bc1 = self._bytecodes[i]
-            len1 = Bytecodes.get_bytecode_length(bc1)
+            len1 = bytecode_length(bc1)
 
             if i + len1 >= len(self._bytecodes):
                 # we're over target, so just copy bc1

src/som/vmobjects/object.py

@@ -89,6 +89,9 @@ class Object(object):
     def send_escaped_block(self, block, universe, interpreter):
         arguments = (block, )
         self.send("escapedBlock:", arguments, universe, interpreter)
+    
+    def is_invokable(self):
+        return False
 
     def __str__(self):
         return "a " + self.get_class().get_name().get_string()

src/som/vmobjects/primitive.py

 from som.vmobjects.object    import Object
-from som.vmobjects.invokable import Invokable
 
-import types
-
-class Primitive(Object, Invokable):
+class Primitive(Object):
     
     # Static field indices and number of primitive fields
     SIGNATURE_INDEX            = 1 + Object.CLASS_INDEX
@@ -30,6 +27,12 @@ class Primitive(Object, Invokable):
 
     def is_primitive(self):
         return True
+    
+    def is_invokable(self):
+        """In the RPython version, we use this method to identify methods 
+           and primitives
+        """
+        return True
 
     def get_signature(self):
         # Get the signature by reading the field with signature index