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Cc: Paul G <paul@rusko.us>,
 internals@lists.php.net
Date: Fri, 30 Jul 2004 16:27:25 -0400
To: Shaun Thomas <sthomas@townnews.com>
X-Mailer: Apple Mail (2.618)
Subject: Re: [PHP-DEV] GOTO operator
From: jeff@procata.com (Jeff Moore)


On Jul 30, 2004, at 10:35 AM, Shaun Thomas wrote:

> Paul G wrote:
>
>> function pseudocode()
>> {
>>     $a=3Dallocate_resource_z();
>>     $b=3Dallocate_resource_y();
>>     $res=3Ddo_stuff();
>>     if(!$res)
>>         goto err_out;
>>     $c=3Dallocate_resource_x();
>>     $res=3Ddo_more_stuff();
>>     if(!$res)
>>         goto err_out;
>>     $d=3Dallocate_resource_foo();
>>     $res=3Ddo_even_more_stuff();
>>     if(!$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=20=

> requires a goto to be efficient.  You could do the same thing with=20
> try/catch/throw:
>
> function pseudocode()
> {
>   $a=3Dallocate_resource_z();
>   $b=3Dallocate_resource_y();
>
>   try {
>     $res=3Ddo_stuff();
>     if(!$res)
>       throw SOME_ERROR;
>
>     $c=3Dallocate_resource_x();
>     $res=3Ddo_more_stuff();
>     if(!$res)
>       throw SOME_ERROR;
>
>     $d=3Dallocate_resource_foo();
>     $res=3Ddo_even_more_stuff();
>     if(!$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 =3D allocate_resource_z();
         $b =3D allocate_resource_y();
         $res =3D do_stuff();
         $c =3D allocate_resource_x();
         $res =3D do_more_stuff();
         $d =3D allocate_resource_foo();
         $res =3D do_even_more_stuff();
     } catch ( Exception $e ) {
         free_resouce($a);
         free_resouce($b);
         if(isset($c)) free_resouce($c);
         if(isset($d)) free_resouce($c);
  =A0 =A0 =A0 =A0throw ($e);
     }
}

Where did the if statements go?  do_stuff(), do_more_stuff(),  and=20
do_even_more_stuff() should throw exceptions rather than return boolean=20=

error indicators.  (Following the principle of raising the error as=20
soon as it can be detected.)  This implementation of pseudocode() also=20=

re-throws the exception, rather than use a boolean error return value. =20=

One major benefit of exceptions is to eliminate conditional statements=20=

as error codes "bubble up."  goto does not help with this.=20=