[Gstreamer-bugs] [Bug 113258] Changed - gst_caps_intersect() returns NULL for empty intersection

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http://bugzilla.gnome.org/show_bug.cgi?id=113258

Changed by ds at schleef.org.

--- shadow/113258	Thu May 29 17:03:26 2003
+++ shadow/113258.tmp.5084	Thu May 29 17:15:46 2003
@@ -24,6 +24,24 @@
 I don't think it's wrong. Basically, NULL as caps on a pad template or
 as a return value of _getcaps() means 'anything', but NULL as an
 intersection means 'nothing' - the combination of these still means
 'anything'.
 
 This is somewhat insonsistent, but it makes sense.
+
+------- Additional Comments From ds at schleef.org  2003-05-29 17:15 -------
+No, it still doesn't make sense. :)
+
+It is easy to generate a case where
+gst_caps_intersect(a,gst_caps_intersect(b,c)) and
+gst_caps_intersect(gst_caps_intersect(a,b),c) return different values.
+
+Looking at it from a set theory perspective, we use NULL to indicate
+both the empty set (curiously also called the null set), and the union
+of all sets.  This plays much havoc with our set operations.  We also
+use NULL to indicate the end of chained caps.
+
+I'd like to change my recommendation to define a GST_CAPS_ANY to
+indicate the union of all possible caps, which might not be NULL.  In
+any case, we should probably start using GST_CAPS_ANY and
+GST_CAPS_NONE instead of NULL.
+