You can do it in any OO language easily as well. For instance, in Python: class UnsafeString: def __init__(self, str): self._str = str self.

You can do it in any OO language easily as well. For instance, in Python: class UnsafeString: def __init__(self, str): self._str = str self._sanitized = None def __str__(self): return self.sanitize() def unsafe(self): return self._str def sanitize(self): if self._sanitized != None: return self._sanitized else: self._sanitized = sanitize(self._sanitized) return self._sanitized That way, as long as you wrap all input in the UnsafeString class, you'll have to be explicit if you want the unsafe version and you'll get the safe version by default.