rfc:instanceof_improvements

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rfc:instanceof_improvements [2020/05/19 18:55] – created maxsemrfc:instanceof_improvements [2022/04/18 10:51] (current) – Move to withdrawn ilutov
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   * Date: 2020-05-17   * Date: 2020-05-17
   * Author: Max Semenik, maxsem.wiki@gmail.com   * Author: Max Semenik, maxsem.wiki@gmail.com
-  * Status: Draft+  * Status: Withdrawn
   * First Published at: http://wiki.php.net/rfc/instanceof_improvements   * First Published at: http://wiki.php.net/rfc/instanceof_improvements
  
 ===== Introduction ===== ===== Introduction =====
-The elevator pitch for the RFC. The first paragraph of this section will be slightly larger to give it emphasis; please write a good introduction.+As currently implemented, the ''instanceof'' operator is inconsistent. 
 +<code php> 
 +var_dump(new MyClass instanceof MyClass); // true 
 +</code> 
 +So far so good? What if we tried to use a scalar type? They can be specified as parameter types just like class names, right? 
 +<code php> 
 +$x = 123; 
 +var_dump($x instanceof int); // false, right hand side is always treated as a class name 
 +</code>
  
 ===== Proposal ===== ===== Proposal =====
-I'd like to propose to modify ''instanceof'' to support non-object types, as well as expressions on the right:+Make ''instanceof'' support non-object types:
 <code php> <code php>
-'foo' instanceof string            // true +var_dump('foo' instanceof string);      // true 
-'foo' instanceof 'string'          // true +var_dump('foo' instanceof ('string'));  // true 
-$logger instanceof "{$this->loggerType}Logger" +$type = 'string'; 
-$foo instanceof SomeClass::class   // kinda silly - but why the heck not? +var_dump('foo' instanceof $type);       // true
-$foo instanceof $someObject::class // a less silly variation +
 </code> </code>
 +
 +==== Types to support ====
 +This proposal covers only concrete scalar types ''int'', ''float'', ''string'', ''bool'' and ''null''; as well as compound types ''array'', ''object'', ''callable'' and ''iterable''. Other types are intentionally omitted:
 +  * ''mixed'' is pointless because there are easier ways to produce an expression always evaluating to true than ''$something instanceof mixed''.
 +  * ''void'' is kinda obvious, but I'm mentioning it just to be thorough.
 +
 +All attempts to check against these types would evaluate to ''false'' (just as currently) and produce warnings in 8.1, upgraded to fatals in 8.2.
 +
 +  * ''resource'' is not available as a parameter type and is on its way out, so it will be unaffected by this RFC and treated as a class name, available for userspace to use.
 +
 +==== Legacy type aliases ====
 +There are several legacy types, supported only for typecasts: ''(integer)'', ''(double)'', ''(boolean)'' and ''(binary)''. They have never worked for any other situations: e.g. the first parameter of ''function f(integer $x)'' is interpreted as a class called ''integer'', we even started issuing warnings in such situations since 8.0. I propose to extend this kind of treatment to ''instanceof'' too, issuing the same warning.
 +
 +==== Constant expressions on the left hand side ====
 +The current implementation has a shortcut where if there is a constant expression to the left of ''instanceof'', the result is hardcoded as false, since the operator supports only class names on the right and constant expressions can't produce objects. This raises a question: how should be Captain Obvious cases like ''123 instanceof int'' be treated? What about slightly less obvious cases like ''123 instanceof $typeName''? For comparison, I've checked two languages that have approaches to OOP similar to PHP:
 +  * In Java, a variable is required on the left side of ''instanceof''. All types of expressions are disallowed.
 +  * In C#, constant expressions to the left of ''is'' produce a correct result but a compiler warning is issued.
 +  * None of these support type names as strings, so the latter use case has no direct analogs.
 +
 +I can see two possibilities why such constructs might appear in code:
 +  * An clueless developer trying to achieve with ''123 instanceof $type'' something for which ''$type === "int"'' is a better solution.
 +  * A code generator went astray and generates something dubious.
 +
 +Considering this, I don't think that adding support for constant expressions on LHS would do our end users any good. I propose to continue shortcutting such cases to false (just to make sure they don't rely on this) and additionally let the developers know they're doing something wrong with ''E_COMPILE_WARNING''. Upgrade the warning to error in 9.0.
  
 ===== Backward Incompatible Changes ===== ===== Backward Incompatible Changes =====
-What breaks, and what is the justification for it?+This proposal doesn't introduce new syntax, it only affects how some existing code could work by making the operator in some cases return true instead of false or throw warnings. However, since the affected use cases currently don't work (in a sense that they don't produce the result one would expect), existing code to be affected by this should be negligibly hard to come by.
  
 ===== Proposed PHP Version(s) ===== ===== Proposed PHP Version(s) =====
-PHP 8.0.+PHP 8.1.
  
 ===== RFC Impact ===== ===== RFC Impact =====
 ==== To SAPIs ==== ==== To SAPIs ====
-Describe the impact to CLI, Development web server, embedded PHP etc.+None.
  
 ==== To Existing Extensions ==== ==== To Existing Extensions ====
-Will existing extensions be affected?+Don't see a reason why they should.
  
 ==== To Opcache ==== ==== To Opcache ====
-It is necessary to develop RFC's with opcache in mind, since opcache is a core extension distributed with PHP. +None.
- +
-Please explain how you have verified your RFC's compatibility with opcache. +
- +
-==== New Constants ==== +
-Describe any new constants so they can be accurately and comprehensively explained in the PHP documentation.+
  
 ===== Open Issues ===== ===== Open Issues =====
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 ===== Unaffected PHP Functionality ===== ===== Unaffected PHP Functionality =====
-List existing areas/features of PHP that will not be changed by the RFC. +Anything not related to ''instanceof''.
- +
-This helps avoid any ambiguity, shows that you have thought deeply about the RFC's impact, and helps reduces mail list noise.+
  
 ===== Future Scope ===== ===== Future Scope =====
-This section details areas where the feature might be improved in future, but that are not currently proposed in this RFC.+I'm currently pondering about extending type casts which would also improve type system and make syntax more consistent, but it's currently brewing in my head and I'm not going to let it out just yet.
  
 ===== Proposed Voting Choices ===== ===== Proposed Voting Choices =====
-What should be done about this (improve instanceof / add new operator / reject this RFC)?+Accept this RFC (y/n, 2/3 majority required)?
  
 ===== Patches and Tests ===== ===== Patches and Tests =====
-Links to any external patches and tests go here. +* WIP patch: https://github.com/php/php-src/pull/6694
- +
-If there is no patch, make it clear who will create a patch, or whether a volunteer to help with implementation is needed. +
- +
-Make it clear if the patch is intended to be the final patch, or is just a prototype. +
- +
-For changes affecting the core language, you should also provide a patch for the language specification.+
  
 ===== Implementation ===== ===== Implementation =====
rfc/instanceof_improvements.1589914546.txt.gz · Last modified: 2020/05/19 18:55 by maxsem

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