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--- rfc:deprecate_curly_braces_array_access [2019/03/25 08:49] – rjhdby
+++ rfc:deprecate_curly_braces_array_access [2019/08/10 23:19] (current) – derick
@@ Line 1: / Line 1: @@
-====== PHP RFC: Deprecate curly braces syntax for accessing array element and string offset. ======
+====== PHP RFC: Deprecate curly brace syntax for accessing array elements and string offsets ======
-  * Version: 0.9
   * Date: 2019-03-12
-  * Author: Andrey Gromov, andrewgrom@rambler.ru
+  * Author: Andrey Gromov <andrewgrom@rambler.ru>, Theodore Brown <theodorejb@outlook.com>
-  * Status: Under Discussion
+  * Status: Implemented (in PHP 7.4)
-  * First Published at: https://wiki.php.net/rfc/deprecate_curly_braces_array_access?do=edit
   * Discussion: https://externals.io/message/104744
+  * Targets: PHP 7.4
+  * Implementation: https://github.com/php/php-src/pull/4416
 ===== Introduction =====
-<blockquote>Both square brackets and curly braces can be used interchangeably for accessing array elements (e.g. $array[42] and $array{42} will both do the same thing in the example above).</blockquote>
+PHP allows both square brackets and curly braces to be used interchangeably
+for accessing array elements and string offsets. For example:
-===== Proposal =====
+<code php>
-Deprecate curly braces syntax for accessing array element and string offset.
+$array = [1, 2];
+echo $array[1]; // prints 2
+echo $array{1}; // also prints 2
+$string = "foo";
+echo $string[0]; // prints "f"
+echo $string{0}; // also prints "f"
+</code>
+However, supporting both of these syntaxes can be confusing. Are there
+circumstances where one syntax behaves differently than the other? Is
+there a difference in performance between them? Is there some difference
+in scoping, since curly braces are the standard way to separate scope?
+What's the purpose of the curly brace syntax?
-Reasons to deprecate curly braces syntax::
+Apart from two short notes in the PHP Manual, the curly brace syntax is
-  - Two ways to do the same thing.
+virtually undocumented. Furthermore, it has reduced functionality
-  - It is very rarely used nowadays.
+compared to the normal bracket syntax. For example, it cannot be used for
-  - It is almost not documented. There is only two short "NOTE" about it.
+pushing an element into an array:
-  - Also, this syntax has reduced functionality. You can't use it for pushing element into array "$arr{} = 1;", creating array "$a={1,2};" or in other similar cases.
-  - Deprecation and following removal will free this syntax for other features. For example: array/string slice, absolute offset access, "windows" (like "slice" in GoLang), etc.
-  - Furthermore, curly braces is standard way to separate scope in almost all languages including PHP (except one very rare and special case).
----------------------
 <code php>
-<?php
+$array[] = 3;
-$arr=[1,2,3];
+echo $array[2]; // prints 3
-var_dump($arr{1});
+$array{} = 3; // Parse error: syntax error, unexpected '}'
 </code>
-Output
+Nor can it be used to create an array:
-<code>
-Warning: Array and string offset access syntax with curly braces is deprecated in /root/php-src/1.php on line 4
+<code php>
-int(2)
+$array = [1, 2]; // works
+$array = {1, 2}; // Parse error: syntax error, unexpected '{'
 </code>
-===== Discussion =====
+It can't be used for list assignment, either:
-== Disagree ==
+<code php>
-<blockquote>Do I understand it right, that you're proposing deprecating accessing $string{$offset}? I think that's an important way of differentiation between string and array offset access.
+[$one, $two] = $array; // works
-I'd vote "yes" for splitting syntax on array and string offset access, but as is: -1.</blockquote>
+{$one, $two} = $array; // Parse error: syntax error, unexpected ','
-<blockquote>I personally use it because I like to quickly tell if I am doing an operation on a string or array, it is eye candy and makes a lot of sense. I think if anything the two syntaxes should be decoupled instead.
+</code>
-From a usage PoV, then from personal experience (outside my own projects), I have seen many usages of this syntax, even as late as my
-current company with a growing codebase that is nearing 1.1m LoC, I have seen this syntax used countless of times. In fact I don't think I
-have been working with a code base where I have not seen this syntax used.
-I have asked fellow developers around in my community today and they have no strong opinion on either, but do like the distinction between.</blockquote>
+===== Proposal =====
+Deprecate curly brace syntax for accessing array elements and string offsets.
-== Agree ==
+<code php>
-<blockquote>I'm okay with this. This syntax has already been deprecated once, though it was reverted for reasons I don't remember.
+$arr = [1, 2, 3];
+var_dump($arr{1});
+</code>
-There are some people using this syntax to distinguish between array and string access. It's a nice thought, but as the vast majority of code doesn't make this distinction (I think the only time I saw this in recent years was inside some old PEAR code), it's not really a useful indicator. The rarity of its use also makes it rather confusing. While $foo[$x] is well established as an array or string offset (or for that matter, ArrayObject) access and will be recognized by any programmer coming from any number of programming languages, $foo{$x} certainly is not, and is a WTF moment for people who don't happen to personally use this syntax.
+Output:
-I'd prefer to phase out this syntax entirely and not reuse it for any other purpose. Reusing syntax is generally a not so good idea, because it means that the same syntax has different meaning in different PHP version.</blockquote>
+<code>
-<blockquote>Four thoughts:
+Deprecated: Array and string offset access syntax with curly braces is deprecated in test.php line 3
+int(2)
+</code>
-. I cannot think of any reason to separate them. If you want to make sure you are indexing a string, do a type check, not bake {} into only working on strings.
+===== Discussion =====
+==== Wasn't the curly brace syntax deprecated once before? ====
+According to an internals discussion from June 2008 (see references
+below), the curly brace syntax was deprecated in PHP 5.1 RC5, but the
+deprecation warning was removed before the final release. In August
+, the documentation for ''$str{42}'' read "deprecated as of PHP 6",
+but again the deprecation never made it into a production release.
-. While Kalle says pretty much every codebase they've seen lately has used {} for indexing, I have never seen a codebase that used it.
-. In any case, usage of {} can be migrated to [] by a style fixer, right?
+==== Is the curly brace syntax valuable for differentiating string and array offset access? ====
+It has been suggested that the duplicate syntax is useful for differentiating
+string and array offset access. The problem with this is that no distinction
+is enforced by the language. Both syntaxes can be used for both arrays and
+strings, so while one codebase might always use ''$str[0]'' for strings and
+''$arr{0}'' for arrays, another codebase might use the opposite convention,
+which leads to more confusion rather than less.
-. Even if we deprecate {}, I don't think we'd be in any hurry to remove it, though with an automatic fixer this seems doable, if we care to do it at all.</blockquote>
+To make sure that code is indexing a string and not an array, a type check
+should be used instead of relying on syntax that can be used for both strings
+and arrays (and thus doesn't tell you anything about the underlying type).
-===== Backward Incompatible Changes =====
-Yes.
-===== Proposed PHP Version(s) =====
+==== How frequently is the curly brace syntax used? ====
-PHP 7.4
+Nikita Popov checked the top 2k Composer packages, and found ~2.2k
+individual uses of the curly brace array syntax. Compared to the 888.3k
+total array accesses in the data set, usage of the alternative syntax is
+about 0.25%. However, even this number is inflated somewhat due to
+duplicate packages (for example, there are two packages that mirror the
+WordPress Core repository, each with 182 usages). 92% of usages in the
+top 2k packages are in just 25 unique projects.
-===== Future Scope =====
-Change to E_COMPILE_ERROR in PHP 8.0.
-Remove in PHP 8.1.
-===== Voting =====
+==== Will it be too much work for people to migrate code away from the curly brace syntax? ====
-/3 majority will be required.
+A migration script has been implemented alongside the deprecation patch:
+https://gist.github.com/theodorejb/763b83a43522b0fc1755a537663b1863
-===== Patches and Tests =====
-https://github.com/php/php-src/compare/PHP-7.4...rjhdby:deprecate_alternate_array_access
+===== Backward Incompatible Changes =====
+A deprecation warning will be output when using the curly brace syntax
+to access array or string offsets.
+===== Vote =====
+Started 3 July 2019. Ends 17th July 2019
+<doodle title="Deprecate curly brace array and string offset syntax in PHP 7.4" auth="rjhdby" voteType="single" closed="true">
+   * Yes
+   * No
+</doodle>
+===== Future Scope =====
+Remove the feature entirely (replacing the deprecation warning
+with a compiler error) in PHP 8 or another future release.
+===== References =====
+Current discussion: https://externals.io/message/104744 and https://externals.io/message/106130.
-Migration script.
+Discussion about deprecation in June 2008: https://externals.io/message/38153.
-https://github.com/rjhdby/php-src/blob/deprecate_alternate_array_access/convert_array_access_braces.php
+Discussion about deprecation in November 2005: https://externals.io/message/20143.

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