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bpo-31443: Formulate the type slot initialization rules in terms of C99. (#3688)

This commit is contained in:
Stefan Krah 2017-09-22 17:44:58 +02:00 committed by GitHub
parent 5e02c7826f
commit ca72589bfa
2 changed files with 15 additions and 14 deletions
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11
Doc/extending/newtypes.rst
View File

@ -177,16 +177,9 @@ the module. We'll expand this example later to have more interesting behavior.
For now, all we want to be able to do is to create new :class:`Noddy` objects.
To enable object creation, we have to provide a :c:member:`~PyTypeObject.tp_new` implementation.
In this case, we can just use the default implementation provided by the API
function :c:func:`PyType_GenericNew`. We'd like to just assign this to the
:c:member:`~PyTypeObject.tp_new` slot, but we can't, for portability sake, On some platforms or
compilers, we can't statically initialize a structure member with a function
defined in another C module, so, instead, we'll assign the :c:member:`~PyTypeObject.tp_new` slot
in the module initialization function just before calling
:c:func:`PyType_Ready`::
function :c:func:`PyType_GenericNew`. ::
noddy_NoddyType.tp_new = PyType_GenericNew;
if (PyType_Ready(&noddy_NoddyType) < 0)
return;
PyType_GenericNew, /* tp_new */
All the other type methods are *NULL*, so we'll go over them later --- that's
for a later section!

18
Modules/xxmodule.c
View File

@ -308,7 +308,7 @@ static PyTypeObject Null_Type = {
0, /*tp_dictoffset*/
0, /*tp_init*/
0, /*tp_alloc*/
0, /* see PyInit_xx */ /*tp_new*/
PyType_GenericNew, /*tp_new*/
0, /*tp_free*/
0, /*tp_is_gc*/
};
@ -338,11 +338,19 @@ PyDoc_STRVAR(module_doc,
static int
xx_exec(PyObject *m)
{
/* Due to cross platform compiler issues the slots must be filled
* here. It's required for portability to Windows without requiring
* C++. */
/* Slot initialization is subject to the rules of initializing globals.
C99 requires the initializers to be "address constants". Function
designators like 'PyType_GenericNew', with implicit conversion to
a pointer, are valid C99 address constants.
However, the unary '&' operator applied to a non-static variable
like 'PyBaseObject_Type' is not required to produce an address
constant. Compilers may support this (gcc does), MSVC does not.
Both compilers are strictly standard conforming in this particular
behavior.
*/
Null_Type.tp_base = &PyBaseObject_Type;
Null_Type.tp_new = PyType_GenericNew;
Str_Type.tp_base = &PyUnicode_Type;
/* Finalize the type object including setting type of the new type