diff options
Diffstat (limited to 'Demo/metaclasses/Eiffel.py')
-rw-r--r-- | Demo/metaclasses/Eiffel.py | 70 |
1 files changed, 35 insertions, 35 deletions
diff --git a/Demo/metaclasses/Eiffel.py b/Demo/metaclasses/Eiffel.py index 38ee6bc..d9c8a9a 100644 --- a/Demo/metaclasses/Eiffel.py +++ b/Demo/metaclasses/Eiffel.py @@ -4,19 +4,19 @@ For example, class C: def m1(self, arg): - require arg > 0 - return whatever + require arg > 0 + return whatever ensure Result > arg can be written (clumsily, I agree) as: class C(Eiffel): def m1(self, arg): - return whatever + return whatever def m1_pre(self, arg): - assert arg > 0 + assert arg > 0 def m1_post(self, Result, arg): - assert Result > arg + assert Result > arg Pre- and post-conditions for a method, being implemented as methods themselves, are inherited independently from the method. This gives @@ -28,10 +28,10 @@ post-condition with that defined in the derived class', for example: class D(C): def m1(self, arg): - return whatever**2 + return whatever**2 def m1_post(self, Result, arg): - C.m1_post(self, Result, arg) - assert Result < 100 + C.m1_post(self, Result, arg) + assert Result < 100 This gives derived classes more freedom but also more responsibility than in Eiffel, where the compiler automatically takes care of this. @@ -42,13 +42,13 @@ up to the derived class. For example, a derived class that takes away the requirement that arg > 0 could write: def m1_pre(self, arg): - pass + pass but one could equally write a derived class that makes a stronger requirement: def m1_pre(self, arg): - require arg > 50 + require arg > 50 It would be easy to modify the classes shown here so that pre- and post-conditions can be disabled (separately, on a per-class basis). @@ -66,27 +66,27 @@ from Meta import MetaClass, MetaHelper, MetaMethodWrapper class EiffelMethodWrapper(MetaMethodWrapper): def __init__(self, func, inst): - MetaMethodWrapper.__init__(self, func, inst) - # Note that the following causes recursive wrappers around - # the pre-/post-condition testing methods. These are harmless - # but inefficient; to avoid them, the lookup must be done - # using the class. - try: - self.pre = getattr(inst, self.__name__ + "_pre") - except AttributeError: - self.pre = None - try: - self.post = getattr(inst, self.__name__ + "_post") - except AttributeError: - self.post = None + MetaMethodWrapper.__init__(self, func, inst) + # Note that the following causes recursive wrappers around + # the pre-/post-condition testing methods. These are harmless + # but inefficient; to avoid them, the lookup must be done + # using the class. + try: + self.pre = getattr(inst, self.__name__ + "_pre") + except AttributeError: + self.pre = None + try: + self.post = getattr(inst, self.__name__ + "_post") + except AttributeError: + self.post = None def __call__(self, *args, **kw): - if self.pre: - apply(self.pre, args, kw) - Result = apply(self.func, (self.inst,) + args, kw) - if self.post: - apply(self.post, (Result,) + args, kw) - return Result + if self.pre: + apply(self.pre, args, kw) + Result = apply(self.func, (self.inst,) + args, kw) + if self.post: + apply(self.post, (Result,) + args, kw) + return Result class EiffelHelper(MetaHelper): __methodwrapper__ = EiffelMethodWrapper @@ -99,12 +99,12 @@ Eiffel = EiffelMetaClass('Eiffel', (), {}) def _test(): class C(Eiffel): - def m1(self, arg): - return arg+1 - def m1_pre(self, arg): - assert arg > 0, "precondition for m1 failed" - def m1_post(self, Result, arg): - assert Result > arg + def m1(self, arg): + return arg+1 + def m1_pre(self, arg): + assert arg > 0, "precondition for m1 failed" + def m1_post(self, Result, arg): + assert Result > arg x = C() x.m1(12) ## x.m1(-1) |