Re: [PHP-DEV] GOTO operator

Shaun Thomas Fri, 30 Jul 2004 07:35:51 -0700

Paul G wrote:

function pseudocode()
{
    $a=allocate_resource_z();
    $b=allocate_resource_y();

    $res=do_stuff();
    if(!$res)
        goto err_out;

    $c=allocate_resource_x();
    $res=do_more_stuff();
    if(!$res)
        goto err_out;

    $d=allocate_resource_foo();
    $res=do_even_more_stuff();
    if(!$res)
        goto err_out;

    return true;

err_out:
    free_resouce($a);
    free_resouce($b);
    if(isset($c)) free_resouce($c);
    if(isset($d)) free_resouce($c);

    return false;
}

While this is valid, it's not really a good example of pseudocode that requires a goto to be efficient. You could do the same thing with try/catch/throw:

function pseudocode()
{
  $a=allocate_resource_z();
  $b=allocate_resource_y();

  try {
    $res=do_stuff();
    if(!$res)
      throw SOME_ERROR;

    $c=allocate_resource_x();
    $res=do_more_stuff();
    if(!$res)
      throw SOME_ERROR;

    $d=allocate_resource_foo();
    $res=do_even_more_stuff();
    if(!$res)
      throw SOME_ERROR;

    return true;
  }

  catch SOME_ERROR {
    free_resouce($a);
    free_resouce($b);
    if(isset($c)) free_resouce($c);
    if(isset($d)) free_resouce($c);

    return false;
  }
}

This is also one of the reasons languages like Ada have named code blocks for exceptions. Here's some ada-like pseudo-code:

BEGIN

  a := allocate_resource_z();
  b := allocate_resource_y();

  res := do_stuff();

  if (!res)
    raise some_exception;

  c := allocate_resource_x();
  res := =do_more_stuff();

  if (!res)
    raise some_exception;

  d := allocate_resource_foo();
  res := do_even_more_stuff();

  if(!res)
    raise unknown;

  return TRUE;

EXCEPTION

  free_resouce(a);
  free_resouce(b);
  if (c) free_resouce(c);
  if (d) free_resouce(c);

  return FALSE;

END

The case that Ilia and the other main developers is not for cases like this. If you look through the Linux kernel, you can see very good examples of goto usage that is not related to this kind of error handling. It's mainly to jump around inside parsing code while maintaining a stack, so the same chunk of code can continuously handle the same source of input without hundreds of if statements and indented blocks.

--
Shaun M. Thomas                INN Database Administrator
Phone: (309) 743-0812          Fax  : (309) 743-0830
Email: [EMAIL PROTECTED]    Web  : www.townnews.com

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Re: [PHP-DEV] GOTO operator

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