2021-11-28 | Paul Boddie | raw annotate files changeset graph | Introduced support for values that can be allocated on a special thread-local stack, copied around and overwritten/mutated, demonstrating the concept using integer and floating-point numbers. Various complications arise with special attributes (such as __data__) due to the way references are tagged to indicate mutable values, and attribute slots must be cleared in locals, objects and fragments before values are stored since target slots are tested for mutable values. | tagged-address-values |
1 class A: 2 def __init__(self, x): 3 self.x = x 4 def __sub__(self, other): 5 return self.x - other.x 6 7 class B: 8 def __init__(self, x): 9 self.x = x 10 def __rsub__(self, other): 11 return other.x - self.x 12 13 class C: 14 def __init__(self, x): 15 self.x = x 16 17 a = A(10) 18 b = B(5) 19 c = C(3) 20 21 print a - b # 5 22 print c - b # -2 23 print a - c # 7 24 25 try: 26 print b - c # should raise an exception 27 except TypeError: 28 print "b - c: b and c do not respectively support the __sub__ and __rsub__ operations"