While this is a cool and useful extension for the ?: operator I'd prefer we didn't use it.  First, it's poorly documented, the only place I could find it is here: http://tigcc.ticalc.org/doc/gnuexts.html#SEC71 .  Second it's not a part of the C standard (ANSI, 89, or 99), it's a GNU C extension.  I'm not sure which flavor of C Objective-C specifies as its base, if any, but I suspect it isn't explicitly GNU C.  The fact that this compiles is probably an accident due to Apple using the clang compiler, if this changes in the future this code could potentially break.  Finally, since this isn't standard syntax it's unlikely other developers will have encountered it and it isn't immediately obvious how it works (if the condition is true is the value NIL, 0, the first operand?  All these are reasonable interpretations).