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From: "Robert Martin" <rmartin@oma.com>
Subject: Re: Software landmines (loops)
Date: 1998/08/31
Message-ID: <6sfq27$fuo$1@hirame.wwa.com>#1/1
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Newsgroups: comp.lang.eiffel,comp.object,comp.software-eng,comp.lang.ada
Date: 1998-08-31T00:00:00+00:00
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Robert I. Eachus wrote in message ...
>
>   Finalization did end up in Ada 95, and it is the right solution to
>this particular problem.

I am not sure of the semantics of 'finalization' in ADA9X, but if it works
like Java's, then it does not solve the problem created by multiple exits
from loops.  Again, the issue is structure.  When a single-entry/single-exit
model is followed, the code attains a structure that is conducive to
resource management.  Consider:  (C++ with a finally clause (which I wish it
had!))

int f()
{
  char* p = 0;
  File* f = 0;
  try{
    p = malloc(80);
    if (!p) return 1;

    f = fopen("myFile", "r");
    if (!f) return 2;

    fread(f, p, 80);
    ...
    return 0;
  }
  finally{
    if (f) fclose(f);
    if (p) free(p);
  }
}


The problem with this is the tests in the finally clause.  Those tests are
an artifact due to loss of structure.  They take time, space, and are not
general (i.e. there might be no reasonable test to perform!)

On the other hand:

int f()
{
  int retval = 0;
  if (char* p = malloc(80))
  {
    if (File* f = fopen("myFile", "r");
    {
      fread(f, p, 80);
      ...
      fclose(f);
    }
    else // fopen failure
    {
      retval = 2;
    }
    free(p);
  }
  else // malloc failure
  {
    retval = 1;
  }
  return retval;
}

No tests necessary, structure preserved.


Robert C. Martin    | Design Consulting   | Training courses offered:
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14619 N Somerset Cr | Tel: (800) 338-6716 |   C++
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"One of the great commandments of science is:
    'Mistrust arguments from authority.'" -- Carl Sagan