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Date: Fri, 23 Jan 2015 12:01:42 +0900
Message-ID: <CAGa2bXYvcS2Z2q+K9e91DBLJEiXMw03Q9MSRP7HgjZtnRJHvAA@mail.gmail.com>
To: Niklas Keller <me@kelunik.com>
Cc: "internals@lists.php.net" <internals@lists.php.net>
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Subject: Re: [PHP-DEV] in Operator
From: yohgaki@ohgaki.net (Yasuo Ohgaki)

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Hi Niklas,

On Mon, Jan 19, 2015 at 9:42 AM, Niklas Keller <me@kelunik.com> wrote:

> I'd like to propose a new feature to PHP: The in Operator
> Bob mentioned a few weeks ago he wants such an operator in PHP and today I
> stumbled over
>
> http://nikic.github.io/2012/07/27/How-to-add-new-syntactic-features-to-PHP.html
> again,
> which uses the in operator as a sample.
>
> Use cases:
>
> $obj = new StdClass;
> $obj->prop = "value";
> $languages = ["PHP", "C", "Java"];
> var_dump("PHP" in $languages); // true
> var_dump("Python" in $languages); // false
> var_dump(0 in $languages); // false
> var_dump("0x0" in ["0e3"]); // false
> var_dump("prop" in $obj); // true
> var_dump("foo" in $obj); // false
> var_dump("Hello" in "Hello World!"); // true
>
> For strings, it would replace `strpos("Hello World!", "Hello") !== false)`,
> for arrays it would replace `in_array($needle, $haystack, true)`
> and for objects it would be a replacement of property_exists($class,
> $property)`.
>
> This change would mainly be syntax sugar, but I think it's worth because:
>  * `"0x0" in ["0e3"]` would return false while `in_array("0x0", ["0e3"])`
> returns true, that's probably an edge case, but there may be a lot of
> people that don't use the `$strict` parameter, see http://3v4l.org/0K7E5
>  * It would solve the issue that it's hard to remember the order of the
> arguments for in_array and strpos, just had to look it up again.
>
> Bob would volunteer to implement that feature.
>

I would like to reserve 'in' and 'out' for Design by Contract (DbC).
http://en.wikipedia.org/wiki/Design_by_contract

D language has in and out like

function foo() {
in {
   // precondition
}
out {
  // postcondition
}
{
  // function body
}

Contract programing can be done only with assert or annotation.
However, it's much easier/readable with native language support.
Contract programming is proved to be fast/robust/secure.

in operator can be useful, but it's the same as in_array().
If we need strict type check, we may do

$ php -r 'var_dump(in_array("0x0", ["0e3"], TRUE));'
bool(false)

as you mentioned.

I would like to reserve 'in' for DbC rather than syntax sugar.

Regards,

--
Yasuo Ohgaki
yohgaki@ohgaki.net

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