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In-Reply-To: <cb6614f6-5dea-7baa-114f-7e719ebfb53a@gmx.de>
Date: Sat, 12 Nov 2016 16:56:13 +0000
Message-ID: <CADVQu1S+hAZFuinqmz_QsdGP=28wwBj6VXQ-KMRPpMV7q9aq4w@mail.gmail.com>
To: "Christoph M. Becker" <cmbecker69@gmx.de>, =?UTF-8?Q?Lauri_Kentt=C3=A4?= <lauri.kentta@gmail.com>
Cc: "internals@lists.php.net >> PHP Internals" <internals@lists.php.net>, Andrea Faulds <ajf@ajf.me>
Content-Type: multipart/alternative; boundary=94eb2c1913b69c227305411d7c42
Subject: Re: [PHP-DEV] [RFC] Interval Comparison
From: dave+php@mudsite.com (David Walker)

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On Sat, Nov 12, 2016 at 9:47 AM Christoph M. Becker <cmbecker69@gmx.de>
wrote:

> On 12.11.2016 at 17:21, David Walker wrote:
>
> > Should
> > $a = 1;
> > var_dump(1 < $a++ < 3);
> >
> > (expanded into numbers) be evaluated as:
> > 1 < 2 && 2 < 3 - True
> > or
> > 1 < 2 && 3 < 3 - False
>
> In my opinion, that should evaluate to
>
>   1 < 1 // false
>
> because we have a post-increment operator, and it seems to me that the
> expansion defined for Python[1] makes most sense:
>

Double my oops, I meant a pre-increment.


>
> > Comparisons can be chained arbitrarily, e.g., x < y <= z is
> > equivalent to x < y and y <= z, except that y is evaluated only once
> > (but in both cases z is not evaluated at all when x < y is found to
> > be false).
>
> [1] <https://docs.python.org/2/reference/expressions.html#not-in>
>

I concur with this, that each term should only be evaluated once, in more
what Lauri defined:
a < ($tmp1 = b) && $tmp1 < ($tmp2 = c) && $tmp2 < d

Which would ensure that each position is evaluated once, in a left->right
fashion.  And I doubly concur that evaluation is short circuited (per my
wrong example, you corrected):

$a = 0
1 < $a++ < $a++ < 3   ~~ 1 < 1 // false. $a would be 1 after this line.
--
Dave

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