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Reply-To: truth@proposaltech.com
To: Jason Garber <jason@ionzoft.com>
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In-Reply-To: <476507566.20041208023930@ionzoft.com>
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Date: Wed, 08 Dec 2004 08:24:01 -0800
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Subject: Re: [PHP-DEV] Isset question
From: truth@proposaltech.com (Todd Ruth)

Here is one reason: $x = @$y[3];
What should isset($x) return if $y doesn't have an
index 3?

If php had distinct concepts of "undefined" (perhaps
this would be a software level undefined value) and
"null" (perhaps this would be a built-in user level 
undefined value), things would work very differently.  
In the example above $x would be "undefined" as would 
any unused variable, and there would be a way to check
whether a variable was undefined.  If you never use
null as a handy way to indicate user level undefinedness,
you won't have any problem with the lack of distinction.
"null" _is_ php's "undefined".  As such, it makes sense
for $x to be null and isset to return false.  If you 
try to use "null" to indicate, for example, that the user 
hasn't yet responded to a question (or that a value from a
database was "null"), you will likely have moments of 
frustration.

That sounded biased, so I have to point out that
making the aforementioned distinction is not a
panacea.  It assumes only two layers: software and
user.  Even if the distinction were made, if the software
had 2 or more layers, you could still end up with
the same issues.  There would need to be conversions
between undefined and null at the layer boundaries.

I'm typically just a lurker here and have only
contributed a few lines of code (and those didn't
even make it in), so these are just the observations
of a user that has played with the internals a bit.

- Todd

On Tue, 2004-12-07 at 23:39, Jason Garber wrote:
> Hello internals,
> 
>   If anyone has a moment to answer this, it'd be appreciated...
> 
>   --
>   isset($x);  => false
>   is_null($x) => Notice: undefined variable $x
> 
>   --
>   $x = null;
>   isset($x);  => false
>   is_null($x) => true
> 
>   The question is *why* does isset() report false on a variable that
>   is set to NULL?  Is there any way to tell if a variable isset and
>   is_null without generating an error?
> 
>   It doesn't seem that this behavior is consistent with the meaning of
>   isset(), or the errors that are generated when a variable is not set.
> 
>   
>   Thanks.
>   
> -- 
> Best regards,
>  Jason Garber                      mailto:jason@ionzoft.com
>  IonZoft, Inc.