Each object carries around a table of associations from strings to pointers. This function lets you set an association.
If the object already had an association with that name, the old association will be destroyed.
key is converted to a
GQuark using g_quark_from_string().
This means a copy of
key is kept permanently (even after
object has been
finalized) — so it is recommended to only use a small, bounded set of values
key in your program, to avoid the
GQuark storage growing unbounded.