Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:75218
Mailing-List: contact internals-help@lists.php.net; run by ezmlm
Received-SPF: error (pb1.pair.com: domain dds.nl from 85.17.251.144 cause and error)
Date: Thu, 3 Jul 2014 13:30:07 +0200 (CEST)
To: Lazare Inepologlou <linepogl@gmail.com>
cc: "internals@lists.php.net" <internals@lists.php.net>
In-Reply-To: <CAMyk_AZJx3UuX3WfMcuw0dtHVOt66xJLueJJt+MZyNXy-AR8iw@mail.gmail.com>
Message-ID: <alpine.LNX.0.999.1407031318460.2935@swan.dds.nl>
References: <alpine.LNX.0.999.1407031108350.526@swan.dds.nl>
 <CAMyk_AZJx3UuX3WfMcuw0dtHVOt66xJLueJJt+MZyNXy-AR8iw@mail.gmail.com>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; format=flowed; charset=UTF-8
Subject: Re: [PHP-DEV] not_null function
From: xen@dds.nl (Xen)

On Thu, 3 Jul 2014, Lazare Inepologlou wrote:

> Well, there is a better alternative:
>
> if ( $x === null ) ....
> if ( $x !== null ) ....
>
> This syntax has also the advantage that it is marginally faster as there is
> neither a function call nor a negation involved.
> :)


This is semantically wrong because a programmer testing for not-null is 
not testing for the negation of is-null.

That is because null is not really a value. It is the absence of value. 
The absence of any value is not the negation of the presence of a 
....value that doesn't exist.

In the programmer's mind, "null" CAN have a value indeed but in that case 
he has picked it himself. In that case it would be semantically sound for 
him to check ($a == null).

But most of the time you don't want to know whether something is null, you 
want to know whether something has any value other than null (whether it 
has a value at all).

Therefore, usually, checking "$a != null" is not entirely meaningful 
because you don't really care about that value you are mentioning, it has 
no meaning to you. This is what makes it meaningless.

All of the terms in a sentence must have meaning for the entire sentence 
to have full meaning.

The absence of any value is a meaningful concept that ought to be directly 
testable. But you test it by asking for the /presence/ of any value. And 
if you *did* want to test for the absence, you would ask

"does it have any value?"

Just try to say this in English:

"doesn't the cup have anything in it?" or
"does the cup not have anything in it?"

You can see the meaning changes completely from what you intend.

In natural language you don't do that. You say

"/IS THERE A PRESENCE/" or "is there a contents"? You don't ask for the 
negation of the negative, because it has a very different meaning.