rfc:deprecate_curly_braces_array_access
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rfc:deprecate_curly_braces_array_access [2019/03/12 14:53] – created rjhdby | rfc:deprecate_curly_braces_array_access [2019/08/10 23:19] (current) – derick | ||
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- | ====== PHP RFC: Deprecate curly braces | + | ====== PHP RFC: Deprecate curly brace syntax for accessing array elements and string |
- | * Version: 0.9 | + | |
* Date: 2019-03-12 | * Date: 2019-03-12 | ||
- | * Author: Andrey Gromov, andrewgrom@rambler.ru | + | * Author: Andrey Gromov |
- | * Status: | + | * Status: |
- | * First Published at: https://wiki.php.net/rfc/deprecate_curly_braces_array_access? | + | * Discussion: https://externals.io/message/104744 |
- | + | * Targets: | |
- | This is a suggested template for PHP Request for Comments (RFCs). Change this template to suit your RFC. Not all RFCs need to be tightly specified. | + | * Implementation: |
- | Read https://wiki.php.net/rfc/howto carefully! | + | |
===== Introduction ===== | ===== Introduction ===== | ||
- | < | + | PHP allows both square brackets and curly braces |
+ | for accessing array elements | ||
- | ===== Proposal ===== | + | <code php> |
- | Deprecate curly braces syntax for accessing | + | $array |
+ | echo $array[1]; // prints 2 | ||
+ | echo $array{1}; // also prints 2 | ||
- | Show compile warning when used. | + | $string = " |
+ | echo $string[0]; // prints " | ||
+ | echo $string{0}; // also prints " | ||
+ | </ | ||
+ | |||
+ | 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? | ||
+ | |||
+ | Apart from two short notes in the PHP Manual, the curly brace syntax is | ||
+ | virtually undocumented. Furthermore, | ||
+ | compared to the normal bracket syntax. For example, it cannot be used for | ||
+ | pushing an element into an array: | ||
<code php> | <code php> | ||
- | <?php | + | $array[] |
- | $arr=[1,2,3]; | + | echo $array[2]; // prints 3 |
+ | $array{} = 3; // Parse error: syntax error, unexpected ' | ||
+ | </ | ||
+ | |||
+ | Nor can it be used to create an array: | ||
+ | |||
+ | <code php> | ||
+ | $array = [1, 2]; // works | ||
+ | |||
+ | $array = {1, 2}; // Parse error: syntax error, unexpected ' | ||
+ | </ | ||
+ | |||
+ | It can't be used for list assignment, either: | ||
+ | |||
+ | <code php> | ||
+ | [$one, $two] = $array; // works | ||
+ | |||
+ | {$one, $two} = $array; // Parse error: syntax error, unexpected ',' | ||
+ | </ | ||
+ | |||
+ | |||
+ | ===== Proposal ===== | ||
+ | Deprecate curly brace syntax for accessing array elements and string offsets. | ||
+ | |||
+ | <code php> | ||
+ | $arr = [1, 2, 3]; | ||
var_dump($arr{1}); | var_dump($arr{1}); | ||
</ | </ | ||
- | Output | + | Output: |
- | < | + | |
- | Warning: Array and string offset access syntax with curly braces is deprecated in / | + | < |
+ | Deprecated: Array and string offset access syntax with curly braces is deprecated in test.php line 3 | ||
int(2) | int(2) | ||
- | |||
</ | </ | ||
+ | |||
+ | ===== 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 | ||
+ | 2006, the documentation for '' | ||
+ | but again the deprecation never made it into a production release. | ||
+ | |||
+ | |||
+ | ==== 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 '' | ||
+ | '' | ||
+ | which leads to more confusion rather than less. | ||
+ | |||
+ | 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' | ||
+ | |||
+ | |||
+ | ==== How frequently is the curly brace syntax used? ==== | ||
+ | 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. | ||
+ | |||
+ | |||
+ | ==== Will it be too much work for people to migrate code away from the curly brace syntax? ==== | ||
+ | A migration script has been implemented alongside the deprecation patch: | ||
+ | https:// | ||
+ | |||
===== Backward Incompatible Changes ===== | ===== Backward Incompatible Changes ===== | ||
- | Yes. | + | A deprecation warning will be output when using the curly brace syntax |
+ | to access array or string offsets. | ||
- | ===== Proposed PHP Version(s) | + | ===== Vote ===== |
- | PHP 7.4 | + | Started 3 July 2019. Ends 17th July 2019 |
+ | <doodle title=" | ||
+ | * Yes | ||
+ | * No | ||
+ | </ | ||
===== Future Scope ===== | ===== Future Scope ===== | ||
- | Change to compile | + | Remove the feature entirely (replacing the deprecation warning |
- | + | with a compiler | |
- | ===== Patches and Tests ===== | + | |
- | https://github.com/php/php-src/compare/master...rjhdby: | + | ===== References ===== |
+ | Current discussion: | ||
- | Not sure if it is good realisation. Also maybe need to change warning | + | Discussion about deprecation in June 2008: https:// |
+ | Discussion about deprecation in November 2005: https:// | ||
rfc/deprecate_curly_braces_array_access.1552402385.txt.gz · Last modified: 2019/03/12 14:53 by rjhdby