rfc:object-initializer

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rfc:object-initializer [2019/09/05 10:26] – Added future scope additional info brzuchalrfc:object-initializer [2019/10/24 07:36] (current) – closing vote, moving to declined brzuchal
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   * Version: 1.0   * Version: 1.0
   * Date: 2019-09-03   * Date: 2019-09-03
-  * Author: Michał Brzuchalski <michal.brzuchalski@gmail.com+  * Author: Michał Brzuchalski <brzuchal@php.net
-  * Status: Draft+  * Status: Declined
   * First Published at: http://wiki.php.net/rfc/object-initializer    * First Published at: http://wiki.php.net/rfc/object-initializer 
- 
- 
  
 ===== Introduction ===== ===== Introduction =====
-PHP doesn't have a convenient literal syntax for creating an object and initializing properties. This makes creating objects and initializing its state quite laborious. Every time you have to:+PHP doesn't have a convenient literal syntax for creating an object and initializing properties. This makes creating objects and initializing their state quite laborious. Every time you have to:
  
   - Instantiate an object.   - Instantiate an object.
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   - Pass created a fully initialized object.   - Pass created a fully initialized object.
  
-That's where object initializer optimization can benefit with single expression statement and it can be used to initialize any kind of object //(including anonymous classes)//. The initializer block can use any properties and variables available in the containing scope, but one has to be wary of the fact that initializers are run before constructors.+In current PHP implementation with Typed Properties, it is possible to instantiate class which doesn't require nullability for all properties and when they're not initialized we finish with 
 +properties in an uninitialized state. 
 + 
 +That's where object initializer optimization can benefit with single expression statement and it can be used to initialize any kind of object //(including anonymous classes)// ensuring all 
 +required properties are properly initialized, otherwise a ''RuntimeExpection'' is thrown 
 + 
 +The initializer block can use any properties and variables available in the containing scope, but one has to be wary of the fact that initializers are run after constructors.
  
 ===== Proposal ===== ===== Proposal =====
-Object initializers allow to assign values to any accessible properties of an object at creation time without having to invoke a constructor followed by lines of assignment statements. The object initializer syntax enables to specify arguments for a constructor or omit the arguments (and parentheses syntax)+Object initializers allow assigning values to any accessible properties of an object at creation time without having to invoke a constructor followed by lines of assignment statements. The object initializer syntax enables to specify arguments for a constructor or omit the arguments (and parentheses syntax).
- +
-The following example shows how to use an object initializer with a named type, Car and how to invoke the parameterless constructor.+
  
 <code php> <code php>
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   public $id;   public $id;
   public $name;   public $name;
 +  private DateTimeImmutable $createdAt;
 +  
 +  public function __construct()
 +  {
 +    $this->createdAt = new DateTimeImmutable("now");
 +  }
 } }
- 
-$customer = new Customer { 
-  id = 123, 
-  name = "John Doe", 
-}; 
  
 class Car class Car
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   public string $vin;   public string $vin;
 } }
 +</code>
 +
 +The following example shows how to use an object initializer with a ''Customer'', ''Car'' and how to invoke the parameterless constructor.
 +
 +<code php>
 +<?php
 +
 +$customer = new Customer {
 +  id = 123,
 +  name = "John Doe",
 +};
  
 $car = new Car { $car = new Car {
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 </code> </code>
  
-The object initializers syntax allows to create an instanceand after that, it assigns the newly created objectwith its assigned properties, to the variable in the assignment.+> **Note!** If in current scope there are constants with exactly the same name as property names used in the above examplethey do not impact object initialization in any way. Property names used in Object Initializer block stay with no relation to constants names.
  
-Above example is an equivalent to the previous one.+The following example is equivalent to the previous one.
  
 <code php> <code php>
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 The main difference is that object initializers allow creating a new object, with its assigned properties in a single expression. For eg. factory methods where normally a significant amount of argument has default values or simple Data Transfer Objects could benefit. The main difference is that object initializers allow creating a new object, with its assigned properties in a single expression. For eg. factory methods where normally a significant amount of argument has default values or simple Data Transfer Objects could benefit.
 +
 +> **Note!** Currently, language allows instantiating object and initializing only a subset of typed non-nullable properties without a default value. These rules apply to object initializer the same way, meaning the creation of properly initialized object state is in authors responsibility, cause object initializer is a simplification as mentioned before.
 +
 +==== Restrictions ====
 +Using Object Initializer enforce that if a class is instantiated with the Object Initializer, at the end of the instantiation and properties initialization, all visible properties //(depends on initialization scope)// are initialized, otherwise, a ''RuntimeException'' is thrown. 
 +This helps to avoid bugs where a property is added to the class but forgot to be assigned it a value in all cases where the class is instantiated and initialized. 
 +
 +The object initializers syntax allows to create an instance, and after that, it assigns the newly created object, with its assigned properties, to the variable in the assignment.
 +
 +<code php>
 +<?php
 +
 +$customer = new Customer {
 +  name = "John Doe",
 +}; // throws RuntimeException: Initialization of Customer class object failed due to missing required properties
 +
 +$car = new Car {
 +  yearOfProduction = 2019,
 +}; // throws RuntimeException: Initialization of Car class object failed due to missing required properties
 +</code>
 +
 +
 +==== Constructors ====
 +Due to the fact that initializer block purpose is a simplification of instantiating and initializing object properties, constructors are called before initialization takes apart. Constructors allow initializing default values //(especially not scalar one properties like ''DateTime'' etc.)// for read-only properties which are visible only in the class scope.
 +
 +Due to the fact that objects in PHP simply have constructor directly declared in class definition or indirectly through the defaulting constructor, creating a class instance and initializing properties through initializer block will effect in invoking constructor and assign property values after instantiation.
 +
 +> **Note!** Object instantiation allows only constructors without required arguments to be used. Any class which requires passing arguments to constructor cannot be used in combination with object initializer. 
 +
 +
 +<code php>
 +<?php
 +
 +class Customer
 +{
 +  public int $id;
 +  public string $name;
 +  private DateTimeImmutable $createdAt;
 +  
 +  public function __construct()
 +  {
 +    $this->createdAt = new DateTimeImmutable("now");
 +  }
 +}
 +
 +$customer = new Customer {
 +  id = 123,
 +  name = "John Doe",
 +};
 +</code>
 +
 +
 +
 +> **Note!** Classes without constructor desired to mimick "structs" or "data classes" are almost completely viable through the class with typed properties which means they rather don't need a constructor declared directly in the definition of class.
 +
 +> **Note!** If a class needs validation upon to validate its invariants a proper validation logic needs to be called after initialization. To combine it with object initializer and keep the validation process encapsulated, instantiation and initialization of class state are possible in named constructor with validation invoke before the instance is being used.
  
 ==== Lexical scope ==== ==== Lexical scope ====
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 Initializer block allows assigning values to properties accessible from the current class context. This means if used to initialize object properties from inside the same class like for eg. using named static constructor all standard visibility rules apply as it is just a simplification of object creation and assigning values statements. Initializer block allows assigning values to properties accessible from the current class context. This means if used to initialize object properties from inside the same class like for eg. using named static constructor all standard visibility rules apply as it is just a simplification of object creation and assigning values statements.
  
-Above example shows the correct behaviour of visibility rules.+The following example shows the correct behaviour of visibility rules.
  
 <code php> <code php>
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 ==== Magic methods ==== ==== Magic methods ====
-An object initializer is just a simplification of instantiating an object and initializing property values that's why all rules regarding properties apply.+ 
 +Due to lacks of property accessors magic methods like set() are often used to keep invariants 
 +and restrict property values to valid ones. This leads potentially to more issues than benefit but at current implementation, language allows using them. 
 + 
 +An object initializer is just a simplification of instantiating the object and initializing property values  
 +that's why all rules regarding assigning property values to apply.
  
 Using an object initializer combined with magic set method call might be used if an additional validation is required. Using an object initializer combined with magic set method call might be used if an additional validation is required.
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 class EmailAddress class EmailAddress
 { {
-  private string $email;+  protected string $email;
   public ?string $name = null;   public ?string $name = null;
          
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 Initializer block stands instead of constructor arguments which means in case of anonymous classes that place is right before the class definition. Initializer block stands instead of constructor arguments which means in case of anonymous classes that place is right before the class definition.
  
-Above example shows how to use object initializer with anonymous classes.+The following example shows how to use object initializer with anonymous classes.
  
 <code php> <code php>
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 Dynamic properties can be set by their name or by a variable which holds the name of property. Dynamic properties can be set by their name or by a variable which holds the name of property.
  
-Above example shows how to use object initializer with dynamic properties.+The following example shows how to use object initializer with dynamic properties.
  
 <code php> <code php>
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 </code> </code>
  
 +===== Backward Incompatible Changes =====
 +This proposal changes the meaning of the above example which uses a curly brace to fetch array offset //(which is already deprecated since PHP 7.4)// which is very rare usage.
  
 +<code php>
 +<?php
  
-===== Backward Incompatible Changes ===== +class Foo {}  
-None+$foo [123 => Foo::class]; 
 +new $foo { 
 +  $var 123 
 +}; 
 +</code> 
 + 
 +===== Reflection ===== 
 +Both ''ReflectionClass'' and ''ReflectionObject'' get a new method ''newInstanceFields(array $fields): object''. 
 + 
 +<code php> 
 +<?php 
 + 
 +$reflectionClass = new ReflectionClass(Customer::class); 
 +$customer = $reflectionClass->newInstanceFields(['name' => 'Bert']); 
 +// equivalent to 
 +$customer = new Customer {name = 'Bert'}; 
 +</code>
  
 ===== Proposed PHP Version(s) ===== ===== Proposed PHP Version(s) =====
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 ==== New Constants ==== ==== New Constants ====
 None.  None. 
- 
- 
-===== Open Issues ===== 
-Calling ctor before or after initializer or using a ctor at all is not resolved yet. 
-Calling zero args ctor might be an option.  
- 
  
 ===== Future Scope ===== ===== Future Scope =====
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 As this is a language change, a 2/3 majority is required. As this is a language change, a 2/3 majority is required.
  
-The vote is a straight Yes/No vote for accepting the RFC and merging the patch.+The vote is a straight Yes/No vote for accepting the RFC. 
 + 
 +<doodle title="Accept object initializer?" auth="brzuchal" voteType="single" closed="true"> 
 +   * Yes 
 +   * No 
 +</doodle> 
 +
 +<doodle title="Choose between two tokens as an assign operator in object initializer block?" auth="brzuchal" voteType="single" closed="true"> 
 +   * = 
 +   * => 
 +</doodle> 
  
 ===== Patches and Tests ===== ===== Patches and Tests =====
rfc/object-initializer.1567679199.txt.gz · Last modified: 2019/09/05 10:26 by brzuchal