Re: [Swarm-Support] objective-c vs. java

[Marcus G. Daniels]

Steve Railsback wrote:

> what you mean by "dynamic method dispatch"? Do you just mean using 
> more method calls than necessary, or using code where the method to be 
> called is a variable? Or something else?

Bad things are things like [self getPos] in the middle of a loop, where 
getPos just returns an instance variable.   The cost of looking up the 
method to call is much more than the work done by the method.  In those 
circumstances, you want to set things up like:

id <UniformIntegerDist> dist =
   [UniformIntegerDist create: globalZone
         setGenerator: randomGenerator
         setIntegerMin: 0
         setMax: 100];
int (*func) (id obj, SEL sel) =
 (int (*) (id obj, SEL sel)) [(id) dist methodFor: M(getIntegerSample)];

And call like:

for (i = 0; i < 1000000000; i++)  func(dist, M(getIntegerSample))

instead of:

for (i = 0 ; i < 1000000000; i++) [dist getIntegerSample];

Some methods take long enough to run that the cost of looking up their 
code isn't a factor.   For example, the same code with doubles instead 
of integers will spend most of the execution time computing the samples.