rfc:list_default_value

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rfc:list_default_value [2015/11/09 12:41] – reezerfc:list_default_value [2017/09/22 13:28] (current) – external edit 127.0.0.1
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-====== PHP RFC:  Default Value in List Syntax ======+====== PHP RFC:  Default Value in List Assignment Syntax ======
   * Version: 0.1   * Version: 0.1
   * Date: 2015-11-08   * Date: 2015-11-08
   * Author: Reeze Xia, reeze@php.net   * Author: Reeze Xia, reeze@php.net
-  * Status: Draft+  * Status: Under Discussion
   * First Published at: http://wiki.php.net/rfc/list_default_value   * First Published at: http://wiki.php.net/rfc/list_default_value
  
 ===== Introduction ===== ===== Introduction =====
-We could destruct variables from an array with [[http://php.net/list| list constuct]], it may be nested or a simple array. But there is no guarantee that the array can fulfill all variables, it will be simple assigned with null with notice error (not good). We will need several redundant code to handle the possible cases if we want to check it and assign it with default values.+We could destruct variables from an array with [[http://php.net/list| list constuct]], it may be nested or a simple array. But there is no guarantee that the array can fulfill all variables, it will be simple assigned with null with notice error (not good). We will need several redundant code to handle the possible cases if we want to check it and assign it with default values. 
  
-For the similar purpose we introduced  [[http://php.net/manual/en/language.operators.comparison.php#language.operators.comparison|Null coalesce "??"]] and [[http://php.net/manual/en/language.operators.comparison.php#language.operators.comparison.ternary|Ternary Operator "?:"]] to help write clean code.+For the similar reason we introduced  [[http://php.net/manual/en/language.operators.comparison.php#language.operators.comparison|Null coalesce "??"]] and [[http://php.net/manual/en/language.operators.comparison.php#language.operators.comparison.ternary|Ternary Operator "?:"]] to help write clean code.
  
 Some clever users figured out  some workaround like this  [[http://php.net/manual/en/function.list.php#113189|User contributed notes]]. But that is not good enough and ugly. Some clever users figured out  some workaround like this  [[http://php.net/manual/en/function.list.php#113189|User contributed notes]]. But that is not good enough and ugly.
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 ===== Proposal ===== ===== Proposal =====
  
-Support new syntax to set default value for list elements, when there the requested index it not found in array:+Support new syntax to set default values for list elements, when the requested index it is not found in array:
  
 <code php> <code php>
 +// basic syntax
 list($a, $b='default') = [1];      // a = 1, b = 'default' list($a, $b='default') = [1];      // a = 1, b = 'default'
 list($a, $b='default') = [1, 2];  // a = 1, b = 2 list($a, $b='default') = [1, 2];  // a = 1, b = 2
 +
 +//  comparation 
 +list($a, list($b=1, $c=2)) = $arr;
 +// or we need to check it ourself
 +if (!isset($arr[1][0])) {
 +    $arr[1][0] = 1;
 +}
 +if (!isset($arr[1][1])) {
 +    $arr[1][0] = 2;
 +}
 +
 +list($a, list($b, $c)) = $arr;
 +
 +
 +// other examples
 +function say_hello()
 +{
 +    return "Hello";
 +}
 +$name = 'PHP';
 +list($a=say_hello(), $b=$name."7.0") = []; // a = 'Hello', b = 'PHP7.0'
 +
 +list($a, list($b=1, $c=2)) = [1]; // a = 1, b = 1, c = 2
 +
 </code> </code>
  
-This could be considered as a shortcut for:+The assignment could be considered as a shortcut for:
  
 <code php> <code php>
 +
 +list($a, $b='default') = $arr;
 +
 +// equals
 +
 $a = $arr[0]; $a = $arr[0];
 $b = isset($arr[1]) ? $arr[1] : 'default'; $b = isset($arr[1]) ? $arr[1] : 'default';
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-All the features and examples of the proposal.+The syntax is:
  
-To [[http://news.php.net/php.internals/66051|paraphrase Zeev Suraski]], explain hows the proposal brings substantial value to be considered +<code flex> 
-for inclusion in one of the world's most popular programming languages.+assignment_list_element: 
 + variable  
 ++ | variable '=' expr # the new syntax. value could be any expression 
 + | T_LIST '(' assignment_list ')' 
 + | /* empty */  
 +</code>
  
-Remember that the RFC contents should be easily reusable in the PHP Documentation.+The syntax is same as function's default value for parameters.
  
-===== Backward Incompatible Changes ===== 
-What breaks, and what is the justification for it? 
  
-===== Proposed PHP Version(s) ===== +We could also set default value in foreach list context:
-List the proposed PHP versions that the feature will be included in.  Use relative versions such as "next PHP 5.x" or "next PHP 5.x.y".+
  
-===== RFC Impact ===== +<code php> 
-==== To SAPIs ==== +foreach($arr as list($k, list($v1='deafult', $v2='default2'))) { 
-Describe the impact to CLI, Development web server, embedded PHP etc.+    // do something 
 +} 
 +</code>
  
-==== To Existing Extensions ==== +More case could be found from PR's tests:  [[https://github.com/php/php-src/pull/1623/files]]
-Will existing extensions be affected?+
  
-==== To Opcache ==== +This feature could also be found in [[https://clojurebridge.github.io/community-docs/docs/clojure/destructuring/|Clojure]] and [[https://hacks.mozilla.org/2015/05/es6-in-depth-destructuring/|Javascript]] for destructing. 
-It is necessary to develop RFC's with opcache in mind, since opcache is a core extension distributed with PHP.+
  
-Please explain how you have verified your RFC's compatibility with opcache.+===== Backward Incompatible Changes =====
  
-==== New Constants ==== +No BC break.
-Describe any new constants so they can be accurately and comprehensively explained in the PHP documentation.+
  
-==== php.ini Defaults ==== +===== Proposed PHP Version(s) ===== 
-If there are any php.ini settings then list: +PHP 7.1
-  * hardcoded default values +
-  * php.ini-development values +
-  * php.ini-production values+
  
-===== Open Issues ===== +===== RFC Impact =====
-Make sure there are no open issues when the vote starts!+
  
-===== Unaffected PHP Functionality ===== +==== To Opcache ====
-List existing areas/features of PHP that will not be changed by the RFC.+
  
-This helps avoid any ambiguity, shows that you have thought deeply about the RFC's impact, and helps reduces mail list noise.+I am working on opcache compatibility. 
 + 
 +===== Open Issues ===== 
 +None for now
  
 ===== Future Scope ===== ===== Future Scope =====
-This sections details areas where the feature might be improved in future, but that are not currently proposed in this RFC. 
  
 ===== Proposed Voting Choices ===== ===== Proposed Voting Choices =====
-Include these so readers know where you are heading and can discuss the proposed voting options. 
  
-State whether this project requires a 2/3 or 50%+1 majority (see [[voting]])+* Whether accept the RFC for PHP 7.1 
 + 
 +This project requires a 2/3 majority (see [[voting]])
  
 ===== Patches and Tests ===== ===== Patches and Tests =====
-Links to any external patches and tests go here. 
  
-If there is no patch, make it clear who will create a patch, or whether a volunteer to help with implementation is needed.+* Patch: [[https://github.com/php/php-src/pull/1623]]
  
-Make it clear if the patch is intended to be the final patch, or is just a prototype.+I am working on opcache compatibility
  
 ===== Implementation ===== ===== Implementation =====
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 ===== References ===== ===== References =====
-Links to external references, discussions or RFCs+ 
 +  * Javascript destructing:  [[https://hacks.mozilla.org/2015/05/es6-in-depth-destructuring/]] 
 +  * Clojure destructing [[https://clojurebridge.github.io/community-docs/docs/clojure/destructuring/]]
  
 ===== Rejected Features ===== ===== Rejected Features =====
-Keep this updated with features that were discussed on the mail lists.+ 
 +===== Changelog ===== 
 + 
 +  * v0.1 - Initial version
rfc/list_default_value.1447072915.txt.gz · Last modified: 2017/09/22 13:28 (external edit)

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