rfc:constructor_promotion

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rfc:constructor_promotion [2020/04/28 14:23] – nikicrfc:constructor_promotion [2020/08/01 23:38] (current) – RFC was implemented carusogabriel
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   * Date: 2020-03-26   * Date: 2020-03-26
   * Author: Nikita Popov <nikic@php.net>   * Author: Nikita Popov <nikic@php.net>
-  * Status: Under Discussion+  * Status: Implemented
   * Target Version: PHP 8.0   * Target Version: PHP 8.0
   * Implementation: https://github.com/php/php-src/pull/5291   * Implementation: https://github.com/php/php-src/pull/5291
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 </PHP> </PHP>
  
-It is also not possible to use the ''callable'' type, because it is [[https://wiki.php.net/rfc/typed_properties_v2#callable_type|not supported]] as a property types:+It is also not possible to use the ''callable'' type, because it is [[https://wiki.php.net/rfc/typed_properties_v2#callable_type|not supported]] as a property type:
  
 <PHP> <PHP>
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 While repeating the default value on the property declaration would currently appear harmless, there are forward-compatibility reasons why it is preferable to only specify the default once. While repeating the default value on the property declaration would currently appear harmless, there are forward-compatibility reasons why it is preferable to only specify the default once.
  
-The first is a possible future extension to allow arbitrary expression in parameter and property defaults:+The first is a possible future extension to allow arbitrary expressions in parameter and property defaults:
  
 <PHP> <PHP>
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 As the example indicates, this allows using doc comment based annotations with promoted properties. As the example indicates, this allows using doc comment based annotations with promoted properties.
 +
 +Additionally, two new methods are added:
 +
 +  * ''ReflectionProperty::isPromoted()'' returns true for properties that have been implicitly generated as part of constructor promotion.
 +  * ''ReflectionParameter::isPromoted()'' returns true for parameters that have resulted in the generation of an implicit property as part of constructor promotion.
 +
 +Most reflection code should not care whether properties are generated or not, but this information will allow reconstructing the structure or the original code more easily.
  
 ==== Inheritance ==== ==== Inheritance ====
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 </PHP> </PHP>
  
-An attribute on a promoted property could be interpreted either as an attribute on the parameter only, on the implied property only, or on both the parameter and the property. This RFC proposes to apply the attribute to both the property and parameter. A consuming library can then chose to ignore one of the attributes, if the used attribute is only supported in property position or only in parameter position. The corresponding desugaring is:+This code could desugar in one of four ways: 
 + 
 +  - The attribute is applied only to the parameter. 
 +  - The attribute is applied only to the implied property. 
 +  - The attribute is applied both to the parameter and the property. 
 +  - Attributes on promoted properties are forbidden, due to ambiguity. 
 + 
 +Here are the possible transformations:
  
 <PHP> <PHP>
 +// Option 1: Attribute applies only to parameter.
 +class Test {
 +    public int $prop;
 +    
 +    public function __construct(
 +        <<ExampleAttribute>>
 +        int $prop,
 +    ) {}
 +}
 +
 +// Option 2: Attribute applies only to property.
 class Test { class Test {
     <<ExampleAttribute>>     <<ExampleAttribute>>
     public int $prop;     public int $prop;
 +    
 +    public function __construct(
 +        int $prop,
 +    ) {}
 +}
  
 +// Option 3: Attribute applies to both
 +class Test {
 +    <<ExampleAttribute>>
 +    public int $prop;
 +    
     public function __construct(     public function __construct(
         <<ExampleAttribute>>         <<ExampleAttribute>>
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     ) {}     ) {}
 } }
 +
 +// Option 4: Error, cannot use attributes with constructor parameter promotion.
 </PHP> </PHP>
 +
 +This RFC proposes to use option 3 (applying the attribute to both property and parameter), as it is the most flexible. The ''isPromoted()'' Reflection APIs can be used by attribute validation code to discard the property or parameter attribute, if necessary.
 +
 +However, I consider this to be something of an implementation detail. If further work on attributes prior to the PHP 8 release shows that it would be advantageous to place the attribute only on the property, we should be open to such a change.
  
 ==== Coding Style Considerations ==== ==== Coding Style Considerations ====
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 ===== Vote ===== ===== Vote =====
  
-Yes/No.+Voting started 2020-05-15 and closes 2020-05-29. 
 + 
 +<doodle title="Add support for declaring properties in the constructor signature?" auth="nikic" voteType="single" closed="true"> 
 +   * Yes 
 +   * No 
 +</doodle>
  
rfc/constructor_promotion.1588083833.txt.gz · Last modified: 2020/04/28 14:23 by nikic

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