[Andrew Koenig]
So here's the strategy: If the low-order bit of an integer is *off*, it's really a pointer to the rest of the implementation. If the low-order bit is *on*, then it represents an integral value that can be obtained by doing a one-bit arithmetic right shift.
Yes, it's sleazy. But I imagine it would be much faster than using inheritance.
[Phillip J. Eby]
I imagine it wouldn't, because it'd add an extra test to not only every Py_INCREF and Py_DECREF, but every PyObject_something call.
[Michael Hudson]
It wouldn't have to be that bad if you put the pointer/int thingy in the ob_ival slot.
Not all HW Python runs on is byte-addressed, so the base idea that "the last bit" of a pointer-to-non-trivial-structure is always 0 doesn't get off the ground. C doesn't have an arithmetic right-shift operator either, but that one is easier to worm around (pyport.h already has a Py_ARITHMETIC_RIGHT_SHIFT macro to "do the right thing"). OTOH, the only current Python platform I know of that's word-addressed is the Cray T3E, which also happens to be the only one I know of where C's signed ">>" zero-fills (and is also the only one I know of that has no 16-bit integral type -- the T3E porters had an interesting <wink> time).