rfc:arrow_functions_v2

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rfc:arrow_functions_v2 [2019/03/14 08:58] – Cover more syntax nikicrfc:arrow_functions_v2 [2019/05/01 08:39] – Accepted nikic
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   * Target version: PHP 7.4   * Target version: PHP 7.4
   * Implementation: https://github.com/php/php-src/pull/3941   * Implementation: https://github.com/php/php-src/pull/3941
-  * Status: Under Discussion+  * Status: Accepted
  
 ===== Introduction ===== ===== Introduction =====
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 </PHP> </PHP>
  
-==== Static arrow functions ====+==== $this binding and static arrow functions ====
  
-For the sake of completeness, static arrow functions are supported using the syntax +Just like normal closures, the ''$this'' variable, the scope and the LSB scope are automatically bound when a short closure is created inside a class method. For normal closures, this can be prevented by prefixing them with ''static''. For the sake of completeness this is also supported for arrow functions:
-<php>static fn($x) => $x</php>. A static arrow function, just like a static closure, will not +
-bind the ''$this'' variable.+
  
-Static closures are mainly (exclusively?) used to avoid unnecessary cycles involving ''$this'', +<PHP> 
-which may result in delayed GC.+class Test { 
 +    public function method() { 
 +        $fn = fn() => var_dump($this); 
 +        $fn(); // object(Test)#1 { ... } 
 +         
 +        $fn = static fn() => var_dump($this); 
 +        $fn(); // Error: Using $this when not in object context 
 +    } 
 +} 
 +</PHP> 
 + 
 +Static closures are rarely used: They're mainly used to prevent ''$this'' cycles, which make GC behavior less predictable. Most code need not concern itself with this. 
 + 
 +It has been suggested that we could use this opportunity to change the ''$this'' binding semantics towards only binding ''$this'' if it is actually used inside the closure. Apart from GC effects, this would result in the same behavior. Unfortunately PHP has some implicit uses of ''$this''. For example ''Foo::bar()'' calls may inherit ''$this'' if it is compatible with the ''Foo'' scope. We could only carry out a conservative analysis of potential ''$this'' use, which would be unpredictable from a user perspective. As such, we prefer to keep the existing behavior of always binding ''$this''.
  
 ==== By-value variable binding ==== ==== By-value variable binding ====
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 ===== Vote ===== ===== Vote =====
  
-Simple yes/no vote.+Voting started 2019-04-17 and ends 2019-05-01. A 2/3 majority is required. 
 + 
 +<doodle title="Add arrow functions as described in PHP 7.4?" auth="nikic" voteType="single" closed="true"> 
 +   * Yes 
 +   * No 
 +</doodle>
  
 ===== Discussion ===== ===== Discussion =====
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 <PHP> <PHP>
 $x = 1; $x = 1;
-$fn = () => $x++;+$fn = fn() => $x++;
 $fn(); $fn();
 var_dump($x); // By-value: 1 var_dump($x); // By-value: 1
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 ===== Changelog ===== ===== Changelog =====
  
 +  * 2019-03-14: Clarify $this binding and explain why we're sticking with always-bind behavior.
   * 2019-03-14: Mention ''%%->%%'', ''%%-->%%'', ''_()'' and ''\$x => $x''.   * 2019-03-14: Mention ''%%->%%'', ''%%-->%%'', ''_()'' and ''\$x => $x''.
rfc/arrow_functions_v2.txt · Last modified: 2020/08/01 23:53 by carusogabriel

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