Re: Problem with NSelect

[Alex Lancaster]

[...]

DS> -step {
DS>   id bestLocation;
DS>   id newLocation;
DS>   id <List> emptySpacesList;
DS>   id <List> optionsList; // Will hold a list of possible places to live.
DS>   int i, s;
DS>   int listLength;
DS>   float bestUtility;
DS>   id <NSelect> selector;
DS>   
DS>   selector=[NSelect create: [self getZone]];
DS>   optionsList=[List create: [self getZone]];
DS> 
DS>   [selector select: 5 from: emptySpacesList into: optionsList];

DS> I get the following compiler error: 

DS> Person.m: In function `_i_Person__step':
DS> Person.m:82: warning: method `select:from:into:' not implemented by
DS> protocol.

`select:from:into:' is a *factory* method (identified by the `+' sign
in front of the method name, rather than the usual `-', these are
often known in C++ and Java-land as class-methods:
`System.out.println()' in Java, is an example of a class method)

This means that you don't need to create in *instance* of NSelect and
then call a *instance method*, but you just use call the *class
method* directly on the class name.  Try:

  [NSelect select: 5 from: emptySpacesList into: optionsList];

leaving the protocol declarations in place.  Btw, Object{Loader,Saver}
and QSort in simtools work in the same way.

 --- 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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