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From: "John G. Volan" <johnvolan@sprintmail.com>
Subject: Re: Software landmines (loops)
Date: 1998/09/08
Message-ID: <35F534F6.D3CCE360@sprintmail.com>#1/1
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Date: 1998-09-08T00:00:00+00:00
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duncan@yc.estec.esa.nlx wrote:
> 
> int doSomething(Tree *pTop)
> {
>   int errorCode;
> 
>   if (pTop != NULL)
>   {
>     if (pTop->pChild != NULL)
>     {
>       if (pTop->pChild->pChild != NULL)
>       {
>          /* lots of nesting omitted */
> 
>                          if (pTop->pChild...->pChild != NULL)
>                          {
>                            errorCode = reallyDoSomething(pTop->pChild...->pChild);
>                          } else
>                          {
>                            errorCode = ERRORX;
>       } else
>       {
>         errorCode = ERROR3;
>       }
>     } else
>     {
>       errorCode = ERROR2;
>     }
>   } else
>   {
>     errorCode = ERROR1;
>   }
>   return(errorCode);
> }

For what it's worth, the above could be transformed into:

int doSomething(Tree *pTop)
{
  int errorCode;

  if (pTop == NULL)
  {
    errorCode = ERROR1;
  }
  else if (pTop->pChild == NULL)
  {
    errorCode = ERROR2;
  }
  else if (pTop->pChild->pChild == NULL)
  {
    errorCode = ERROR3;
  }
  ...
  /* lots of nesting omitted */
  ...
  else if (pTop->pChild...->pChild == NULL)
  {
    errorCode = ERRORX;
  }
  else
  {
    errorCode = reallyDoSomething(pTop->pChild...->pChild);
  }
  return(errorCode);
}

As you can see, the nesting has been considerably reduced, yet this
function is still single entry/single exit.  It also shares with the
early-return version the advantage of showing the choice of error-code
close to the test that determines the error.

Best of both worlds? :-)

> int compareThings(Thing *pLeft, Thing *pRight)
> {
>     assert(pLeft != NULL && pRight != NULL);
> 
>     if (pLeft->x != pRight->x)
>     {
>         if (pLeft->x < pRight->x)
>         {
>             return(-1);
>         } else
>         {
>             return(+1);
>         }
>     }
>     if (pLeft->y != pRight->y)
>     {
>        /* similar logic */
>     }
>     /* other members */
>     return(0);
> }

Again, the above can be transformed to:

int compareThings(Thing *pLeft, Thing *pRight)
{
    assert(pLeft != NULL && pRight != NULL);

    int result = 0;

    if (pLeft->x < pRight->x)
    {
        result = -1;
    }
    else if (pLeft->x > pRight->x)
    {
        result = +1;
    }
    else if (pLeft->y < pRight->y)
    {
        result = -1;
    }
    else if (pLeft->y > pRight->y)
    {
        result = +1;
    }
    /* other members */
    else
    {
        result = 0;
    }
    return result;
}

-- 
indexing
   description: "Signatures for John G. Volan"
   self_plug: "Ex Ada guru", "Java 1.1 Certified", "Eiffelist wannabe"
   two_cents: "Java would be even cooler with Eiffel's assertions/DBC, %
              %generics, true MI, feature adaptation, uniform access, %
              %selective export, expanded types, etc., etc..."
class JOHN_VOLAN_SIGNATURE inherit SIGNATURE invariant
   disclaimer: not (opinion implies employer.opinion)
end -- class JOHN_VOLAN_SIGNATURE