TODO: QPDFObject parent idea

TODO

@@ -8,6 +8,29 @@ Before Release:
 * Stay on top of https://github.com/pikepdf/pikepdf/pull/315
 * Release qtest with updates to qtest-driver and copy back into qpdf
 
+Parent pointer idea:
+
+* Have replaceKey, removeKey, and eraseItem return the old values. The
+  comments will clarify the difference between these and the andGet
+  versions.
+* Add std::weak_ptr<QPDFObject> parent to QPDFObject. When adding a
+  direct object to an array or dictionary, set its parent. When
+  removing it, clear the parent pointer.
+* When a direct object that already has a parent is added to
+  something, it is a warning and will become an error in qpdf 12.
+  There needs to be unsafe add methods used by unsafeShallowCopy.
+  These will add but not modify the parent pointer.
+
+This allows an object to be moved from one object to another by
+removing it, which returns the now orphaned object, and then inserting
+it somewhere else. It also doesn't break the pattern of adding a
+direct object to something and subsequently mutating it. It just
+prevents the same object from being added to more than one thing.
+
+Note that arrays and dictionaries still need to contain
+QPDFObjectHandle because of indirect objects. This only pertains to
+direct objects, which are always "resolved" in QPDFObjectHandle.
+
 Next:
 * JSON v2 fixes