rfc:readonly_properties_v2

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rfc:readonly_properties_v2 [2021/06/04 14:26] – nikicrfc:readonly_properties_v2 [2021/07/01 10:16] – nikic
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   * Date: 2021-06-02   * Date: 2021-06-02
   * Author: Nikita Popov <nikic@php.net>   * Author: Nikita Popov <nikic@php.net>
-  * Status: Draft+  * Status: Voting
   * Target Version: PHP 8.1   * Target Version: PHP 8.1
   * Implementation: https://github.com/php/php-src/pull/7089   * Implementation: https://github.com/php/php-src/pull/7089
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 <PHP> <PHP>
 class Test { class Test {
-    public readonly int $prop = 0;+    public function __construct( 
 +        public readonly int $i = 0, 
 +        public readonly array $ary = [], 
 +    ) {}
 } }
  
 $test = new Test; $test = new Test;
-$test->prop += 1; +$test->i += 1; 
-$test->prop++; +$test->i++; 
-++$test->prop; +++$test->i; 
-$ref =& $test->prop; +$test->ary[] = 1; 
-$test->prop =& $ref; +$test->ary[0][] = 1; 
-byRef($test->prop);+$ref =& $test->i; 
 +$test->i =& $ref; 
 +byRef($test->i);
 foreach ($test as &$prop); foreach ($test as &$prop);
 </PHP> </PHP>
Line 259: Line 264:
  
 ''ReflectionProperty::setValue()'' can bypass the requirement that initialization occurs from the scope where the property has been declared. However, reflection cannot modify a readonly property that has already been initialized. ''ReflectionProperty::setValue()'' can bypass the requirement that initialization occurs from the scope where the property has been declared. However, reflection cannot modify a readonly property that has already been initialized.
 +
 +Similarly, closure rebinding can be used to bypass the initialization scope requirement.
 +
 +==== Serialization ====
 +
 +Readonly properties have no impact on serialization. As ''%%__unserialize()%%'' (and the legacy ''Serializable::unserialize()'') method are invoked without a prior constructor call, readonly properties will be in an uninitialized state and can be set by the ''%%__unserialize()%%'' implementation.
 +
 +This also applies to userland serializers and hydrators. As long as the object is created using ''ReflectionClass::newInstanceWithoutConstructor()'' or some other constructor-bypass, it is always safe to initialize readonly properties.
  
 ===== Rationale ===== ===== Rationale =====
  
-The readonly property concept introduced in this proposal provides strong immutability guarantees, which apply both inside and outside the class. Once a property has been initialized, it cannot be changed under any circumstances.+The readonly property concept introduced in this proposal provides strong immutability guarantees, which apply both inside and outside the class. Once a property has been initialized, it cannot be changed under any circumstances. Reading a readonly property will always return the same value, no matter what code runs in between: 
 + 
 +<PHP> 
 +class Test { 
 +    public readonly string $prop; 
 +     
 +    public function method(Closure $fn) { 
 +        $prop = $this->prop; 
 +        $fn(); // Any code may run here. 
 +        $prop2 = $this->prop; 
 +        assert($prop === $prop2); // Always holds. 
 +    } 
 +} 
 +</PHP>
  
 These guarantees are //too// strong for certain use-cases. For example, some classes may wish to have properties that are publicly readable, but can only be written from within the class. This is a much weaker guarantee, as the value of a property can change during the lifetime of an object. //Both// variants can be useful depending on the situation, and the addition of readonly properties neither precludes nor discourages the addition of asymmetric property visibility. These guarantees are //too// strong for certain use-cases. For example, some classes may wish to have properties that are publicly readable, but can only be written from within the class. This is a much weaker guarantee, as the value of a property can change during the lifetime of an object. //Both// variants can be useful depending on the situation, and the addition of readonly properties neither precludes nor discourages the addition of asymmetric property visibility.
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 ===== Vote ===== ===== Vote =====
  
-Yes/No.+Voting started on 2021-07-01 and closes on 2021-07-15. 
 + 
 +<doodle title="Add readonly properties as proposed?" auth="nikic" voteType="single" closed="false"> 
 +   * Yes 
 +   * No 
 +</doodle>
  
rfc/readonly_properties_v2.txt · Last modified: 2021/07/20 15:37 by nikic

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