rfc:readonly_and_immutable_properties

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rfc:readonly_and_immutable_properties [2020/06/21 12:19] – first draft read to get feedback on deciding direction andreromrfc:readonly_and_immutable_properties [2020/06/21 18:47] (current) – formating andrerom
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 **This is a early draft, currently looking for feedback on direction on what would make most sense to propose, especially if there is any point in even exploring using Attributes for the features covered here or not.** **This is a early draft, currently looking for feedback on direction on what would make most sense to propose, especially if there is any point in even exploring using Attributes for the features covered here or not.**
  
-With the introduction of typed properties in PHP 7.4, properties have become far more powerful. However it is currently not possible to specify disconnected write vs read visibility for properties without having to resort to magic methods (getters and setters), for immutable semantic it's even more cumbersome. This requires unnecessary boilerplate, makes usage less ergonomic and hurts performance.+With the introduction of typed properties in PHP 7.4, properties have become far more powerful. However it is currently not possible to specify disconnected write vs read visibility for properties, such as readonly, without having to resort to magic methods (getters and setters). For immutable semantic it's even more cumbersome. This requires unnecessary boilerplate, makes usage less ergonomic and hurts performance.
  
 This RFC resolves this issue by proposing a few options: This RFC resolves this issue by proposing a few options:
   - Language approach:   - Language approach:
     - Change to make it possibility to specify write visibility disconnected from read.     - Change to make it possibility to specify write visibility disconnected from read.
-    - Immutable keyword for immutable semantics on write access+    - readonly keyword for write access, on property and class (implicit all properties) 
 +    - immutable keyword for write access, on property and class (implicit all properties)
   - Attribute approach:   - Attribute approach:
-    - Readonly attribute for properties, if #1.1 is accepted this is merely syntax sugar that adds possibility to set readonly on classes (implicit all properties). +    - Readonly attribute for properties, if #1.1/1.2 is accepted this is merely syntax sugar. 
-    - Immutable attribute for properties, if #1.2 is accepted this is merely syntax sugar that adds possibility to set immutability on classes (implicit all properties). +    - Immutable attribute for properties, if #1.3 is accepted this is merely syntax sugar
- +
- +
-//Unless discussions phase points to clear preference within php internals and broader community, these four proposals will be offered as separate votes. Technically all 4 options can be accepted, however downside is there will be more than one way of doing things. So maybe a discussion on where Attributes fits into the language in the future is needed as well.//+
  
  
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 ==== Readonly ==== ==== Readonly ====
  
-This RFC differs from [[rfc:readonly_properties|Readonly properties]] (2014, withdrawn) by instead using the recently accepted Attribute language feature for annotating Readonly properties. As done in Rust, and in user land annotations in many PHP frameworks.+This RFC aligns with [[rfc:readonly_properties|Readonly properties]] (2014, Withdrawn).
  
  
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-This RFC differs from[[rfc:immutability|Immutability]] (2018, stale) by instead using the recently accepted Attribute language feature for annotating Immutable properties. Aligning with Readonly proposal within this RFC.+This RFC aligns with [[rfc:immutability|Immutability]] (2018, Stale).
  
-This RFC does __not__ align with the semantics of the recent [[rfc:write_once_properties|Write once properties]], which is targeting a different problem.+This RFC does __not__ align with the semantics of the recent [[rfc:write_once_properties|Write once properties]] (2020, Declined), which is targeting a different problem.
  
  
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-This RFC does not try to solve as wider use case as the different iterations of [[rfc:propertygetsetsyntax-v1.2|Property Accessors Syntax]].+This RFC does not try to solve as wide use case as the different iterations of [[rfc:propertygetsetsyntax-v1.2|Property Accessors Syntax]] does.
  
-It's of this author's opinion that property type hinting and accessors where the two main obstacles to previous attempts at adding readonly semantics to PHP properties back in 2012-2014. And while readonly is rather hard to do in a clean way in PHP today, most other use cases offered by Accessors can be accomplished by plain PHP methods. Finally, Accessors overcomplicates readonly use case, and does not solve the needs for immutable property semantics. +However: 
- +- Accessors overcomplicates readonly, and does not offer solutions to immutability 
-Thus the author of this RFC believes what is proposed here should be done before any proposal for Accessors is re-considered, as anything here can be made syntax sugar for Accessors, if it ever gets accepted.+- There seems to be a higher need in the community for readonly and immutable semantics 
 +- Everything Accessors offers beyond disconnected read and write visibility for properties, can easily be done with plain methods. The same is not true for readonly and immutable semantics as shown in the introduction.
  
  
 ===== Proposal ===== ===== Proposal =====
  
-==== 1.1 Language ability to set property visibility for write access ====+==== Common semantics ==== 
 + 
 +== References == 
 + 
 +Attempting to pass a property value outside of allowed writable scope as a reference, results in an error. 
 + 
 + 
 +==== 1. Language Approach ==== 
 + 
 + 
 +=== 1.1 Language ability to set property visibility separately for write access ===
  
 This proposal adds support for enforced write visibility checks for declared properties. The following example illustrates the basic syntax: This proposal adds support for enforced write visibility checks for declared properties. The following example illustrates the basic syntax:
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     public:protected string $name;     public:protected string $name;
          
-    // Property is writeonly in public and protected scope+    // Property is write-only in public and protected scope
     private:public string $newName;     private:public string $newName;
  
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 </code> </code>
  
-The format is "<read_visibility>:<write_visibility>", and if you omit the last visibility value you will like before implicit set both read and write visibility at once _(unless other future keywords or attributes states otherwise).  +The format is "<read_visibility>:<write_visibility>", and if you omit the last visibility value you will like before implicit set both read and write visibility at once _(unless other future keywords or attributes states otherwise).
- +
- +
-== References == +
- +
-Attempting to pass a property value outside of allowed scope as reference, is an error. +
  
  
 == Reflection == == Reflection ==
  
-When using reflection, methods such as "ReflectionProperty::setAccessible()" will work as before, it will implicit set visibility for both read and write.+When using reflection, methods such as ''ReflectionProperty::setAccessible()'' will work as before, it will implicit set visibility for both read and write.
  
 However with this proposal the following existing methods will represent read visibility for cases where it differs: However with this proposal the following existing methods will represent read visibility for cases where it differs:
-- ReflectionProperty::isPrivate +- ''ReflectionProperty::isPrivate()'' 
-- ReflectionProperty::isProtected +- ''ReflectionProperty::isProtected()'' 
-- ReflectionProperty::isPublic+- ''ReflectionProperty::isPublic()''
  
 And for checking separate write visibility the following methods may be used: And for checking separate write visibility the following methods may be used:
-- ReflectionProperty::isWritePrivate — Checks if property is writable in private +- ''ReflectionProperty::isWritePrivate'' — Checks if property is writable in private 
-- ReflectionProperty::isWriteProtected — Checks if property is writable in protected +- ''ReflectionProperty::isWriteProtected'' — Checks if property is writable in protected 
-- ReflectionProperty::isWritePublic — Checks if property is writable in public+- ''ReflectionProperty::isWritePublic'' — Checks if property is writable in public
  
  
-"Reflection::getModifiers()" and "Reflection::getModifierNames()" will need adaption too, and proposal is to adapt it so "getModifierNames()" continues to return the visibility as specified, meaning it may now return for instance "public:protected" as one of the strings returned.+''Reflection::getModifiers()'' and ''Reflection::getModifierNames()'' will need adaption too, and proposal is to adapt it so ''getModifierNames()'' continues to return the visibility as specified, meaning it may now return for instance ''public:protected'' as one of the strings returned.
  
 //TODO: Expand this with modifier ints representing all variations and their names// //TODO: Expand this with modifier ints representing all variations and their names//
  
 +=== 1.2 readonly keyword ===
 +
 +This proposal adds support for runtime-enforced readonly write visibility for declared properties. The following example illustrates the basic syntax:
 +
 +<code php>
 +class User {
 +    // Property is readonly, and can only be written to in protected scope
 +    public readonly int $id;
 +    
 +    // Property is readonly, and can only be written to in private scope
 +    protected readonly string $name;
 +
 +    // [assuming 1.1 is accepted] Invalid declaration (visibility is already stating property is readonly)
 +    public:private readonly string $email;
 +
 +    public function __construct(int $id, string $name) {
 +        $this->id = $id;
 +        $this->name = $name;
 +    }
 +}
 +</code>
 +
 +Keyword can also be set on class level, implicit setting it on all fields unless they have their own immutable attribute:
 +
 +<code php>
 +readonly class User {
 +    // Property is readonly, and can only be written to in protected scope
 +    public int $id;
 +    
 +    // Property is readonly, and can only be written to in private scope
 +    protected string $name;
 +
 +    // [assuming 1.1 is accepted] Invalid declaration (visibility is already stating property is readonly)
 +    public:private string $email;
 +
 +    public function __construct(int $id, string $name) {
 +        $this->id = $id;
 +        $this->name = $name;
 +    }
 +}
 +</code>
 +
 +
 +== Readonly semantics ==
 +
 +An readonly property may only be written to in scope lower than what is define as its read+write visibility, so if visibility is public, it may only be written to in protected scope.
 +
 +
 +== Reflection ==
 +
 +When using reflection, methods such as ''ReflectionProperty::setAccessible()'' will work as before, it will implicit disable readonly flag.
 +
 +Furthermore the following method is proposed added to be able to detect readonly properties:
 +- ''ReflectionProperty::isReadonly()''
 +
 +
 +''Reflection::getModifiers()'' and ''Reflection::getModifierNames()'' will need adaption too to add int and keywords for "readonly".
 +
 +//TODO: Expand this with specific modifier int for "readonly"//
  
  
-=== 1.2 Language ability to set immutable property visibility for write access ===+=== 1.3 immutable keyword ===
  
 This proposal adds support for runtime-enforced immutable write visibility for declared properties. The following example illustrates the basic syntax: This proposal adds support for runtime-enforced immutable write visibility for declared properties. The following example illustrates the basic syntax:
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 class User { class User {
     // Property is immutable, can only be written to in __construct in protected scope     // Property is immutable, can only be written to in __construct in protected scope
-    public immutable string $id;+    public immutable int $id;
  
     // [assuming 1.1 is accepted] Property is immutable, can only be written to in __construct in private scope     // [assuming 1.1 is accepted] Property is immutable, can only be written to in __construct in private scope
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 } }
 </code> </code>
 +
 +Keyword can also be set on class level, implicit setting it on all fields unless they have their own readonly attribute:
 +
 +<code php>
 +immutable class User {
 +    // Property is immutable, can only be written to in during construction in protected scope
 +    public int $id;
 +    
 +    // Property is immutable, can only be written to during construction in private scope
 +    protected string $email;
 +
 +    public function __construct(int $id, string $email) {
 +        $this->id = $id;
 +        $this->email = $email;
 +    }
 +}
 +</code> 
  
  
 == Immutable semantics == == Immutable semantics ==
  
-An immutable property may only be written to in __construct() and in other methods involved in object creation (__set_state, __unserialize, __wakeup, and unserialize), besides that it is allowed to be unset in __destruct(). +An immutable property may only be written to in construct and in other methods involved in object creation (set_state, unserialize, and wakeup), besides that it is allowed to be unset in destruct. 
  
 Unless otherwise specified in visibility, the write/unset access is available within protected scope. Unless otherwise specified in visibility, the write/unset access is available within protected scope.
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 == Reflection == == Reflection ==
  
-When using reflection, methods such as "ReflectionProperty::setAccessible()" will work as before, it will implicit disable immutable flag.+When using reflection, methods such as ''ReflectionProperty::setAccessible()'' will work as before, it will implicit disable immutable flag.
  
 Furthermore the following method is proposed added to be able to detect immutable properties: Furthermore the following method is proposed added to be able to detect immutable properties:
-- ReflectionProperty::isImmutable+- ''ReflectionProperty::isImmutable()''
  
  
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 ==== 2. Attributes ==== ==== 2. Attributes ====
  
-With the recently accepted [[rfc:attributes_v2|Attribute v2 RFC]], another option here, or an supplemental one , would be to use attributes for introducing Readonly and Immutable semantics. Similar to how Rust does with its [[https://docs.rs/readonly/0.1.6/readonly/|readonly create]].+With the recently accepted [[rfc:attributes_v2|Attribute v2 RFC]], another option here, or a supplemental one, would be to use attributes for introducing Readonly and Immutable semantics. Similar to how Rust does with its [[https://docs.rs/readonly/0.1.6/readonly/|readonly create]].
  
 However the Attribute RFC does not allow for what is being drafted here, so this would need suggesting a way for userland classes to tell parser / compiler to enhance language features. However the Attribute RFC does not allow for what is being drafted here, so this would need suggesting a way for userland classes to tell parser / compiler to enhance language features.
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-==== 2.1 Readonly attribute ====+=== 2.1 Readonly attribute ===
  
  
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 class User { class User {
     <<Readonly>>     <<Readonly>>
-    public string $id;+    public int $id;
  
     // This property is not readonly     // This property is not readonly
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 class User { class User {
     // This property is readable in public scope and writeable in protected     // This property is readable in public scope and writeable in protected
-    public string $id;+    public int $id;
          
     // This property is readable in protected scope and writeable in private     // This property is readable in protected scope and writeable in private
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 </code>  </code> 
  
 +//For readonly semantics see proposal 1.2//
  
-== Readonly semantics == 
  
-An readonly property may only be written to in scope lower than what is define as its read+write visibility, so if visibility is public, it may only be written to in protected scope. +== Reflection ==
  
 +//TODO: show example on reading /setting attribute via reflection, and how this relates to "ReflectionProperty::setAccessible()".//
  
-==== 2.2. Immutable attribute ====+ 
 + 
 +=== 2.2. Immutable attribute ===
  
 This proposal adds a compiler attribute which implies a runtime-enforced immutable write visibility checks for declared properties. The following example illustrates the basic syntax: This proposal adds a compiler attribute which implies a runtime-enforced immutable write visibility checks for declared properties. The following example illustrates the basic syntax:
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 class User { class User {
     <<Immutable>>     <<Immutable>>
-    public string $id;+    public int $id;
  
     public string $email;     public string $email;
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 <<Immutable>> <<Immutable>>
 class User { class User {
-    public string $id;+    public int $id;
     public string $email;     public string $email;
  
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-//For immutable semantics see proposal 1.2, when setting the attribute on semantics will be //+//For immutable semantics see proposal 1.3//
  
 == Reflection == == Reflection ==
  
- +//TODO: show example on reading /setting attribute via reflection, and how this relates to ''ReflectionProperty::setAccessible()''.//
-==== 3.0 Class only attribute ==== +
- +
-One third option here, is that if 1.x proposals are accepted, and the proposed attributes in 2.x are accepted but only for being specified on class level, where it adds the capability to affect all properties. +
- +
-Alternative would be to propose class level keyword for "readonly" and "immutable". +
  
  
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 Code that expects to be able to make properties writeable via reflection will have to adapt for new code taking advantage of this. Code that expects to be able to make properties writeable via reflection will have to adapt for new code taking advantage of this.
  
-While ReflectionProperty::setAccessible() will still work like before, checks using isProtected() or isPrivate() won't detect if class has other visibility for write (proposal #1), or take into account specific attributes affecting write (assuming proposal #1 is voted down and Readonly and Immutable becomes own attribute logic instead of merely syntax sugar for #1)+While ''ReflectionProperty::setAccessible()'' will still work like before, checks using ''isProtected()'' or ''isPrivate()'' won't detect if class has other visibility for write (proposal #1), or take into account specific attributes affecting write (assuming proposal #1 is voted down and Readonly and Immutable becomes own attribute logic instead of merely syntax sugar for #1.x)
  
  
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 ===== Performance ===== ===== Performance =====
  
-//Performance tests will need to be done once there is a implementation of this. Then overhead on properties, as well as measuring benefit over using magic methods.//+//Performance tests will need to be done once there is an implementation of this. Then overhead on properties, as well as measuring benefit over using magic methods.//
  
 ===== Vote ===== ===== Vote =====
  
 As this is a language change, a 2/3 majority is required. As this is a language change, a 2/3 majority is required.
-//RFC is in draft, and will undergo discussion phase before it is put for a vote.// 
  
 ===== References ===== ===== References =====
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   * [[https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/language-specification/classes#readonly-fields|C# readonly fields]], semantically similar to what is proposed as "immutable" here.   * [[https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/language-specification/classes#readonly-fields|C# readonly fields]], semantically similar to what is proposed as "immutable" here.
 +  * [[https://docs.rs/readonly/0.1.6/readonly/|Rust readonly create]]
  
  
rfc/readonly_and_immutable_properties.1592741957.txt.gz · Last modified: 2020/06/21 12:19 by andrerom

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