Re: CreateBegin with no createEnd in swarm examples

[Alex Lancaster]

>>>>> "PJ" == Paul Johnson <address@hidden> writes:

[...]

PJ> Hey, this reminded me. In all swarmapps, there is createBegin
PJ> without a create end for the obj.  Look in Heatbugs, for example.
PJ> Its createBegin has this statement:

PJ>   obj = [super createBegin: aZone];

PJ> but there is never obj = [obj createEnd];
 
PJ> What's up with that?  Is obj getting its createEnd indirectly
PJ> through the modelSwarm's createEnd?

PJ> This has been a curiosity to me for a long time and I'm eager to
PJ> know the answer.

If you had an an MyObject class, something like:

+ createBegin: aZone
{
  SomeObject *obj = [super createBegin: aZone];
  obj->someVal = 1;
  
  [...]

  return [obj createEnd];
}

- setSomething: something
{
  [...]
}

- createEnd
{
  [super createEnd];
  return self;
}

And when you created the object, you did the following:

  anObject = [MyObject createBegin: [self getZone]];
  [anObject setSomething: something];
  anObject = [anObject createEnd];

then `createEnd' would get called *twice*, once internally in the
factory method, and the second time by the -createEnd method.

However, if you have a *convenience* method, method (where createBegin
and createEnd are called in the same factory method), then it's
appropriate to have the +createBegin: and -createEnd in the same
method i.e.:

+ create: aZone setSomething: something
{
  SomeObject *obj = [super createBegin: aZone];
  [obj setSomething: something];
  
  return ([obj createEnd]);
}

 --- Alex

-- 
  Alex Lancaster           |  e-mail: address@hidden
  Swarm Program            |     web: http://www.santafe.edu/~alex
  Santa Fe Institute       |     tel: +1-(505) 984-8800 (ext 242)
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