Re: [PHP-DEV] GOTO operator

[Jeff Moore]

On Jul 30, 2004, at 10:35 AM, Shaun Thomas wrote:
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;
  }
}
I would prefer to write the original code as follows:
function pseudocode()  {
    try {
        $a = allocate_resource_z();
        $b = allocate_resource_y();
        $res = do_stuff();
        $c = allocate_resource_x();
        $res = do_more_stuff();
        $d = allocate_resource_foo();
        $res = do_even_more_stuff();
    } catch ( Exception $e ) {
        free_resouce($a);
        free_resouce($b);
        if(isset($c)) free_resouce($c);
        if(isset($d)) free_resouce($c);
        throw ($e);
    }
}
Where did the if statements go?  do_stuff(), do_more_stuff(),  and 
do_even_more_stuff() should throw exceptions rather than return boolean 
error indicators.  (Following the principle of raising the error as 
soon as it can be detected.)  This implementation of pseudocode() also 
re-throws the exception, rather than use a boolean error return value.  
One major benefit of exceptions is to eliminate conditional statements 
as error codes "bubble up."  goto does not help with this. 
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