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Date: Thu, 4 Mar 2021 11:54:58 +0100
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To: Christian Schneider <cschneid@cschneid.com>
Cc: PHP internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Don't compare zero exponentials in strings as equal
From: nikita.ppv@gmail.com (Nikita Popov)

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On Thu, Mar 4, 2021 at 10:54 AM Christian Schneider <cschneid@cschneid.com>
wrote:

> Am 04.03.2021 um 01:37 schrieb Ben Ramsey <ben@benramsey.com>:
> > On Mar 3, 2021, at 14:25, Kamil Tekiela <tekiela246@gmail.com> wrote:
> >>
> >> when both are strings then chances are that this is an error.
> >
> > Except when comparing two values from sources known to provide numbers
> as strings, such as form input and database results. :-)
>
>
> This would be a problem for leading zeroes and leading/training spaces,
> right?
>
> Leading zeroes theoretically could happen in databases, leading/training
> spaces happen in form input and possibly databases.
> Are there other 'common' cases?
>

The main one that comes to mind is something like '0' == '0.0'. However,
the real problem is something else: Comparison behavior doesn't affect just
== and !=, but also < and >. And I can see how people would want '2' < '10'
to be true (numeric comparison) rather than false (lexicographical
comparison).

I generally agree that we should remove the special "numeric string"
handling for equality comparisons, and I don't think that removing that
behavior would have a major impact. But we do need to carefully consider
the impact it has on relational operators. There are two ways I can see
this going:

1. Decouple equality comparison from relational comparison. Don't handle
numeric strings for == and !=, but do handle them for <, >, etc. The
disadvantage is that comparison results may not be trichotomous, e.g. for
"0" op "0.0" all of ==, < and > would return false. (To be fair, this can
already happen in other cases, e.g. non-comparable objects.)

2. Don't allow relational comparison on strings. If you want to compare
them lexicographically, use strcmp(), otherwise cast to number first.
("Don't allow" here could be a warning to start with.)

Regards,
Nikita

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