#include "Python.h"

PyObject *

PyCell_New(PyObject *obj)

{

PyCellObject *op;

op = (PyCellObject *)PyObject_GC_New(PyCellObject, &PyCell_Type);

if (op == NULL)

return NULL;

op->ob_ref = obj;

Py_XINCREF(obj);

_PyObject_GC_TRACK(op);

return (PyObject *)op;

}

PyObject *

PyCell_Get(PyObject *op)

{

if (!PyCell_Check(op)) {

PyErr_BadInternalCall();

return NULL;

}

Py_XINCREF(((PyCellObject*)op)->ob_ref);

return PyCell_GET(op);

}

PyCell_Set(PyObject *op, PyObject *obj)

{

PyObject* oldobj;

if (!PyCell_Check(op)) {

PyErr_BadInternalCall();

return -1;

}

oldobj = PyCell_GET(op);

Py_XINCREF(obj);

PyCell_SET(op, obj);

Py_XDECREF(oldobj);

return 0;

}

static void

cell_dealloc(PyCellObject *op)

{

_PyObject_GC_UNTRACK(op);

Py_XDECREF(op->ob_ref);

PyObject_GC_Del(op);

}

#define TEST_COND(cond) ((cond) ? Py_True : Py_False)

static PyObject *

cell_richcompare(PyObject *a, PyObject *b, int op)

{

int result;

PyObject *v;

/* neither argument should be NULL, unless something's gone wrong */

assert(a != NULL && b != NULL);

/* both arguments should be instances of PyCellObject */

if (!PyCell_Check(a) || !PyCell_Check(b)) {

v = Py_NotImplemented;

Py_INCREF(v);

return v;

}

/* compare cells by contents; empty cells come before anything else */

a = ((PyCellObject *)a)->ob_ref;

b = ((PyCellObject *)b)->ob_ref;

if (a != NULL && b != NULL)

return PyObject_RichCompare(a, b, op);

result = (b == NULL) - (a == NULL);

switch (op) {

case Py_EQ:

v = TEST_COND(result == 0);

break;

case Py_NE:

v = TEST_COND(result != 0);

break;

case Py_LE:

v = TEST_COND(result <= 0);

break;

case Py_GE:

v = TEST_COND(result >= 0);

break;

case Py_LT:

v = TEST_COND(result < 0);

break;

case Py_GT:

v = TEST_COND(result > 0);

break;

default:

PyErr_BadArgument();

return NULL;

}

Py_INCREF(v);

return v;

}

static PyObject *

cell_repr(PyCellObject *op)

{

if (op->ob_ref == NULL)

return PyUnicode_FromFormat("<cell at %p: empty>", op);

return PyUnicode_FromFormat("<cell at %p: %.80s object at %p>",

op, op->ob_ref->ob_type->tp_name,

op->ob_ref);

}

static int

cell_traverse(PyCellObject *op, visitproc visit, void *arg)

{

Py_VISIT(op->ob_ref);

return 0;

}

static int

cell_clear(PyCellObject *op)

{

Py_CLEAR(op->ob_ref);

return 0;

}

static PyObject *

cell_get_contents(PyCellObject *op, void *closure)

{

if (op->ob_ref == NULL)

{

PyErr_SetString(PyExc_ValueError, "Cell is empty");

return NULL;

}

Py_INCREF(op->ob_ref);

return op->ob_ref;

}

cell_set_contents(PyCellObject *op, PyObject *obj)

{

Py_XINCREF(obj);

Py_XSETREF(op->ob_ref, obj);

return 0;

}

static PyGetSetDef cell_getsetlist[] = {

{"cell_contents", (getter)cell_get_contents,

(setter)cell_set_contents, NULL},

{NULL} /* sentinel */

};

PyTypeObject PyCell_Type = {

PyVarObject_HEAD_INIT(&PyType_Type, 0)

"cell",

sizeof(PyCellObject),

0,

(destructor)cell_dealloc, /* tp_dealloc */

0, /* tp_print */

0, /* tp_getattr */

0, /* tp_setattr */

0, /* tp_reserved */

(reprfunc)cell_repr, /* tp_repr */

0, /* tp_as_number */

0, /* tp_as_sequence */

0, /* tp_as_mapping */

0, /* tp_hash */

0, /* tp_call */

0, /* tp_str */

PyObject_GenericGetAttr, /* tp_getattro */

0, /* tp_setattro */

0, /* tp_as_buffer */

Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC, /* tp_flags */

0, /* tp_doc */

(traverseproc)cell_traverse, /* tp_traverse */

(inquiry)cell_clear, /* tp_clear */

cell_richcompare, /* tp_richcompare */

0, /* tp_weaklistoffset */

0, /* tp_iter */

0, /* tp_iternext */

0, /* tp_methods */

0, /* tp_members */

cell_getsetlist, /* tp_getset */

};