Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:109046
To: Mike Schinkel <mike@newclarity.net>
CC: Internals <internals@lists.php.net>
Thread-Topic: [PHP-DEV] RFC idea: Block scoped variables with "let $x =  expr"
Thread-Index: AQHV+veJX4ttr7o+RE+uPBxQ97wSIKhJ+xQCgAA0sACAABcx3g==
Date: Sun, 15 Mar 2020 23:42:41 +0000
Message-ID:
 <DM5PR07MB30674A0E48CA751CD00B9F46F9F80@DM5PR07MB3067.namprd07.prod.outlook.com>
References:
 <DM5PR07MB3067D2DEAD4B3C85FBDFD559F9F80@DM5PR07MB3067.namprd07.prod.outlook.com>
 <fb548f2a-0f0d-4dbe-8b69-b4c94501ecc4@Mikes-iPad-Pro>
 <DM5PR07MB30678914A5A748371901797FF9F80@DM5PR07MB3067.namprd07.prod.outlook.com>,<30C23964-6E52-4B2B-8947-8BD3E9E46354@newclarity.net>
In-Reply-To: <30C23964-6E52-4B2B-8947-8BD3E9E46354@newclarity.net>
Accept-Language: en-CA, en-US
Content-Language: en-CA
x-ms-exchange-messagesentrepresentingtype: 1
x-tmn: [cUpu0dymTOM1HMDa0EZdU2HW2JVhRjtRTtZ9nyKpQVBegyNqDE+AULbPxbpVUHhv]
x-ms-publictraffictype: Email
x-incomingheadercount: 46
x-eopattributedmessage: 0
x-ms-office365-filtering-correlation-id: 10503d5c-673d-40a9-abc8-08d7c93a8d65
x-ms-traffictypediagnostic: BN3NAM04HT034:
x-microsoft-antispam: BCL:0;
x-microsoft-antispam-message-info:
 Jj1uUWyl5BKIFedvBJiy0YisOGbmmt0brj4tLoQCBscnfHh8THVsBSlU0QoY+2XxnIFo5HkKPpFUCh4uPZjOGxJvx4oR0DhWht+mULG3MO2dp2weOBe1XerEhbyc6rEnr4yUsEk+CI8T8Oy9ID2slJinD+4PPhD2AmfBSf4l6PfSKB4DjSOtCroSyWkPa7Z0KswVNq3y/laCAj/Zig9PWsJeyLp2+M7GkaaHje0v30Y=
x-ms-exchange-antispam-messagedata:
 9aOlW6S8Pb78LYCfenap1kf2wSrivrwGY1KlogI0jwwp0A5sMvWlUD9fjrBBYs8tgEXS4DMFQ1+xRPWbdUAcyR8p+HAoQgBi8Oa8baGRg+l8gD2tXecyJCst3RUF67oOLhnyuIjXpZpk1ECA9D0GjLfpdVhVCZg4Z/L6eQneS1gaW3ZflGCqAZebRjTB9Qy3np+mImbDtrt4TEIBqntH1Q==
x-ms-exchange-transport-forked: True
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-OriginatorOrg: hotmail.com
X-MS-Exchange-CrossTenant-RMS-PersistedConsumerOrg: 00000000-0000-0000-0000-000000000000
X-MS-Exchange-CrossTenant-Network-Message-Id: 10503d5c-673d-40a9-abc8-08d7c93a8d65
X-MS-Exchange-CrossTenant-rms-persistedconsumerorg: 00000000-0000-0000-0000-000000000000
X-MS-Exchange-CrossTenant-originalarrivaltime: 15 Mar 2020 23:42:41.3231
 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Internet
X-MS-Exchange-CrossTenant-id: 84df9e7f-e9f6-40af-b435-aaaaaaaaaaaa
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN3NAM04HT034
Subject: Re: [PHP-DEV] RFC idea: Block scoped variables with "let $x =  expr"
From: tysonandre775@hotmail.com (tyson andre)

Hi Mike,=0A=
=0A=
> What I am about to say is ironic since I too often feel people are trying=
 to enforce their view of coding on the world,=0A=
> but I do not think we want to give people tools to make it easier to work=
 with long functions/scripts.=0A=
=0A=
Blocked-scoped variables is a tool which can make short code and long code =
more readable.=0A=
Making it easier to work with long functions is an example of a benefit of =
having block-scoped variables,=0A=
not the main goal of this RFC idea.=0A=
=0A=
https://github.com/getify/You-Dont-Know-JS/blob/1st-ed/scope%20%26%20closur=
es/ch3.md#blocks-as-scopes=0A=
goes into some of the other reasons to use block-scoped variables in JS=0A=
=0A=
- Many languages other than JavaScript/PHP support Block Scope,=0A=
  and so developers from those languages are accustomed to the mindset, whe=
reas those who've primarily only worked in JavaScript may find the concept =
slightly foreign.=0A=
- Block scope is a tool to extend the earlier "Principle of Least Privilege=
 Exposure"=0A=
  from hiding information in functions to hiding information in blocks of o=
ur code.=0A=
- Developers may prefer to check themselves against accidentally (re)using =
variables outside of their intended purpose,=0A=
  such as being issued an error about an unknown variable if you try to use=
 it in the wrong place.=0A=
  Block-scoping (if it were possible) for the `i` variable would make `i` a=
vailable only for the for-loop,=0A=
  causing an error if `i` is accessed elsewhere in the function.=0A=
  This helps ensure variables are not re-used in confusing or hard-to-maint=
ain ways.=0A=
=0A=
> I would be very interested in seeing business logic coded into a long fun=
ction that literally cannot be made better by refactoring into multiple sma=
ller functions.=0A=
> If you have some, please do post to a Gist and share it to see if it in f=
act it cannot be refactored and made "better."=0A=
=0A=
One example is if PHP itself is used for HTML rendering in top-level statem=
ents - pages or components of a page may be spread out across hundreds of l=
ines.=0A=
This could be moved to a different templating engine for PHP instead of raw=
 PHP,=0A=
but the refactoring would be time-consuming and error-prone.=0A=
=0A=
Separately from HTML rendering, some problem domains are just complex.=0A=
For example, consider the functions such as decodeMPEGaudioHeader in=0A=
https://github.com/WordPress/WordPress/blob/master/wp-includes/ID3/module.a=
udio.mp3.php=0A=
(I'm not involved in that project or file)=0A=
=0A=
You could split it up into multiple helper functions, but instead of hundre=
ds of lines in one function for a complicated file format,=0A=
you'd have to jump across even more abstractions/lines to know where XYZ wa=
s set.=0A=
Fully refactoring that might not make ever make business sense,=0A=
but there is a benefit to having the ability to mark if a variable is actua=
lly block-scope or used elsewhere=0A=
(e.g. to have a better idea of if refactoring to a different function is sa=
fe)=0A=
=0A=
> Given the nature of long functions, I think the awkward syntax here provi=
des a nice disincentive to writing overly long functions.=0A=
>=0A=
> But as I said, the closure does exist in case someone absolutely needs to=
 control=0A=
> the scope of a block within an existing long function, such as the 1400 l=
ine function I've been refactoring for months now...=0A=
=0A=
Also, closures aren't a convenient substitute for everything the local scop=
e can do for other reasons.=0A=
E.g. modifying by reference will mask issues with undefined or possibly und=
efined variables when modifying values outside of the closure scope.=0A=
=0A=
```=0A=
function compute_product($values) {=0A=
    // Other lines omitted=0A=
    foreach ($values as $value) {=0A=
        (function() use (&$product, $value) {=0A=
            $letVar =3D $value + 1;=0A=
            // Other lines omitted=0A=
            $product *=3D $letVar;=0A=
        })();=0A=
    }=0A=
    return $product;=0A=
}=0A=
```=0A=
=0A=
This has the bug that $product was never defined, but no notices are emitte=
d because $product gets set to null=0A=
when the reference is taken by reference, and php currently doesn't warn ab=
out multiplying by null.=0A=
=0A=
Using an actual `let $var =3D $value + 1`, this would get the notice for th=
e variable being undefined.=0A=
=0A=
- Tyson=