[1/4] Add gdbpy_borrowed_ref
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This adds new gdbpy_opt_borrowed_ref and gdbpy_borrowed_ref classes.
These class is primarily for code "documentation" purposes -- it makes
it clear to the reader that a given reference is borrowed. However,
they also add a tiny bit of safety, in that conversion to gdbpy_ref<>
will either be rejected (by the "opt" class) or acquire a new
reference.
---
gdb/python/py-ref.h | 80 +++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 80 insertions(+)
@@ -41,6 +41,86 @@ struct gdbpy_ref_policy
template<typename T = PyObject> using gdbpy_ref
= gdb::ref_ptr<T, gdbpy_ref_policy>;
+/* A class representing an optional borrowed reference. It is
+ "optional" because NULL is a valid value.
+
+ This is a simple wrapper for a PyObject*. Aside from documenting
+ what the code does, the main advantage of using this is that
+ conversion to a gdbpy_ref<> is prevented.
+
+ An optional borrowed reference is only used in situations where
+ Python says NULL is valid. For example, it is used as the type of
+ the "keywords" argument to a varargs method. Most code should
+ prefer an ordinary gdbpy_borrowed_ref, see below. */
+class gdbpy_opt_borrowed_ref
+{
+public:
+
+ gdbpy_opt_borrowed_ref (PyObject *obj)
+ : m_obj (obj)
+ {
+ }
+
+ template<typename T>
+ gdbpy_opt_borrowed_ref (const gdbpy_ref<T> &ref)
+ : m_obj (ref.get ())
+ {
+ }
+
+ operator PyObject * ()
+ {
+ return m_obj;
+ }
+
+ operator gdbpy_ref<> () = delete;
+
+protected:
+ PyObject *m_obj;
+};
+
+/* A borrowed reference that is guaranteed not to be NULL.
+
+ Like gdbpy_opt_borrowed_ref, this mostly serves a documentary
+ purpose. However, it also allows a checked cast to any subclass of
+ PyObject, and conversion to a gdbpy_ref<> will automatically
+ acquire a new reference -- a safety improvement over plain
+ PyObject*. */
+class gdbpy_borrowed_ref : public gdbpy_opt_borrowed_ref
+{
+public:
+
+ gdbpy_borrowed_ref (PyObject *obj)
+ : gdbpy_opt_borrowed_ref (obj)
+ {
+ gdb_assert (m_obj != nullptr);
+ }
+
+ template<typename T>
+ gdbpy_borrowed_ref (const gdbpy_ref<T> &ref)
+ : gdbpy_opt_borrowed_ref (ref)
+ {
+ gdb_assert (m_obj != nullptr);
+ }
+
+ gdbpy_borrowed_ref (std::nullptr_t) = delete;
+
+ /* Allow a (checked) conversion to any subclass of PyObject. */
+ template<typename T,
+ typename = std::is_convertible<T *, PyObject *>>
+ operator T * ()
+ {
+ gdb_assert (PyObject_TypeCheck (m_obj, T::corresponding_object_type));
+ return static_cast<T *> (m_obj);
+ }
+
+ /* When converting a borrowed reference to a gdbpy_ref<>, a new
+ reference is acquired. */
+ operator gdbpy_ref<> ()
+ {
+ return gdbpy_ref<>::new_reference (m_obj);
+ }
+};
+
/* A wrapper class for Python extension objects that have a __dict__ attribute.
Any Python C object extension needing __dict__ should inherit from this