Re: [Swarm-Support] gcc and messages to nil. I'm needing help

[Scott Christley]

Hi Paul,

I think if you provide your own implementation of the nil_method function in your code, it will override the one in the ObjC runtime.  This relies upon a linking trick so it may not work on all platforms.  Try adding this into one of your source files

id

nil_method (id receiver, SEL op, ...)

{

  raiseEvent (InvalidArgument,  "The message `%s' was sent to nil.\n",

              sel_get_name (op));

  return nil;

}

then do a method call to nil to see if it works.

Probably it would be a good idea to log a bug/feature request with GCC to allow nil_method to be re-defined by applications; this was done for memory allocation functions that the ObjC runtime uses.

cheers

Scott

On Aug 11, 2006, at 4:26 PM, Paul Johnson wrote:

In the recent past, Swarm programs would stop with an error if a message was sent to nil. 

Now, In Fedora Core 4 and 5, gcc-4.X, the behavior of the compiler has been changed. I think now it matches the behavior described in the Objective-C book that Apple circulates, which holds that messages to nil do not produce a warning or error.  This causes bad bad problems for me/us.  One problem, which we discovered last month, is that even when Swarm's init fails to create lispArchiver and lispAppArchiver, the program continues and generates some bogus outcomes.  Now I noticed while working on an FC4 system that an improperly created distribution was resulting in a nil, and then repeated calls for "getDoubleSample" were returning crap, but no warnings or errors.

So I wish I could make gcc behave like it did in the old days, so that a program would stop and tell us when a message is sent to a nil.  And where in the code it happens. 

pj

-- 

Paul E. Johnson                       email: address@hidden

Dept. of Political Science            http://lark.cc.ku.edu/~pauljohn

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