you can already do exactly that in Python with a bit of evil magic: $ cat evil.py class cast(object): def __init__(self, x): if isinstance(

you can already do exactly that in Python with a bit of evil magic: $ cat evil.py class cast(object): def __init__(self, x): if isinstance(x, cast): self.x = x.x else: self.x = x def __add__(self, other): return other.__class__(self.x) + other def __radd__(self, other): return other + other.__class__(self.x) $ python3 -i evil.py >>> a = 1 >>> b = "2" >>> a + b Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: unsupported operand type(s) for +: 'int' and 'str' >>> cast(a) + b '12' >>> a + cast(b) 3 >>> cast(a) + cast(b) Traceback (most recent call last): File "<stdin>", line 1, in <module> File "evil.py", line 9, in __add__ return other.__class__(self.x) + other File "evil.py", line 9, in __add__ ... repeated many times ... File "evil.py", line 9, in __add__ return other.__class__(self.x) + other RuntimeError: maximum recursion depth exceeded