Re: Questions on the return statement

[Gary Polhill]

Fabio Mascelloni wrote:
> 
> Suppose I declare such an instance variable :
> 
> unsigned  *inst;
> 
> Then I initialize it to some value:
> 
> - intitInstVar:(unsigned) length
> {
>     inst=calloc ( length, sizeof (unsigned));
>     //init in some way with some values
>    return self;
> }
> 
> After that I implement a method that could be invoked by objects of unrelated
> classes and that returns the instance variable:
> 
> -(unsigned *) getInstVar
> {
>    return inst;
> }
> 
> The question is: does getInstVar returns a copy of the object or simply a
> reference to it ?
> If it simply returns a reference, how can I make it return a copy of the
> object ?

something like

-(unsigned *)getInstVar {
   int i;
   unsigned *copyOfInst;

   copyOfInst = calloc(instVarLength, sizeof(unsigned));
                        // instVarLength should be set to length in initInstVar:
   for(i = 0; i < instVarLength; i++)
      copyOfInst[i] = inst[i];
   return copyOfInst;
}

This is a good way to leak memory, however. It would be better to create and
allocate memory for the copy in the calling method -- that way it's easier to
look for variables that have been given memory and not freed. getInstVar would
then be something like:

-(unsigned *)getInstVar: (unsigned *)copyOfInst {
   int i;

   for(i = 0; i < instVarLength; i++)
      copyOfInst[i] = inst[i];
   return copyOfInst;
}

> In J.J Merelo's Breeder there's a method to get the genotype of a chromosome:
> 
> - getGenotype
> {
>     return (id) genotype;
> }
> where genotype is defined as  unsigned char *genotype.Is this the right way?

No, my understanding of Obj-C is a little vague, but as far as I know id
is still a pointer type (even though there's no *), i.e. getGenotype still
returns a reference to, rather than a copy of genotype. The reference has
merely been cast to type id rather than type unsigned char *.

Gary

--

Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen. AB15 8QH
Tel: +44 (0) 1224 318611               Email: address@hidden

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