mirror of https://github.com/python/cpython
bpo-31443: Formulate the type slot initialization rules in terms of C99. (#3688)
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@ -177,16 +177,9 @@ the module. We'll expand this example later to have more interesting behavior.
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For now, all we want to be able to do is to create new :class:`Noddy` objects.
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To enable object creation, we have to provide a :c:member:`~PyTypeObject.tp_new` implementation.
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In this case, we can just use the default implementation provided by the API
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function :c:func:`PyType_GenericNew`. We'd like to just assign this to the
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:c:member:`~PyTypeObject.tp_new` slot, but we can't, for portability sake, On some platforms or
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compilers, we can't statically initialize a structure member with a function
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defined in another C module, so, instead, we'll assign the :c:member:`~PyTypeObject.tp_new` slot
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in the module initialization function just before calling
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:c:func:`PyType_Ready`::
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function :c:func:`PyType_GenericNew`. ::
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noddy_NoddyType.tp_new = PyType_GenericNew;
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if (PyType_Ready(&noddy_NoddyType) < 0)
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return;
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PyType_GenericNew, /* tp_new */
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All the other type methods are *NULL*, so we'll go over them later --- that's
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for a later section!
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@ -308,7 +308,7 @@ static PyTypeObject Null_Type = {
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0, /*tp_dictoffset*/
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0, /*tp_init*/
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0, /*tp_alloc*/
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0, /* see PyInit_xx */ /*tp_new*/
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PyType_GenericNew, /*tp_new*/
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0, /*tp_free*/
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0, /*tp_is_gc*/
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};
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@ -338,11 +338,19 @@ PyDoc_STRVAR(module_doc,
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static int
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xx_exec(PyObject *m)
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{
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/* Due to cross platform compiler issues the slots must be filled
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* here. It's required for portability to Windows without requiring
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* C++. */
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/* Slot initialization is subject to the rules of initializing globals.
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C99 requires the initializers to be "address constants". Function
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designators like 'PyType_GenericNew', with implicit conversion to
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a pointer, are valid C99 address constants.
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However, the unary '&' operator applied to a non-static variable
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like 'PyBaseObject_Type' is not required to produce an address
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constant. Compilers may support this (gcc does), MSVC does not.
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Both compilers are strictly standard conforming in this particular
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behavior.
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*/
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Null_Type.tp_base = &PyBaseObject_Type;
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Null_Type.tp_new = PyType_GenericNew;
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Str_Type.tp_base = &PyUnicode_Type;
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/* Finalize the type object including setting type of the new type
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