rfc:typed_properties_v2

Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revision Previous revision
Next revision
Previous revision
Next revision Both sides next revision
rfc:typed_properties_v2 [2018/09/21 15:40]
nikic Revert incorrect change by third party
rfc:typed_properties_v2 [2019/01/07 14:48]
nikic Add errata: inc/dec overflow
Line 5: Line 5:
   * Proposed PHP version: PHP 7.4   * Proposed PHP version: PHP 7.4
   * Implementation: https://github.com/php/php-src/pull/3313   * Implementation: https://github.com/php/php-src/pull/3313
-  * Status: In voting+  * Discussion: https://externals.io/message/102333 and https://externals.io/message/103148 
 +  * Status: Accepted
  
 ===== Introduction ===== ===== Introduction =====
Line 1245: Line 1246:
 As this is a language change, a 2/3 majority is required. As this is a language change, a 2/3 majority is required.
  
-<doodle title="Add support for typed properties as described in this RFC?" auth="bwoebi" voteType="single" closed="false">+<doodle title="Add support for typed properties as described in this RFC?" auth="bwoebi" voteType="single" closed="true">
    * Yes    * Yes
    * No    * No
 </doodle> </doodle>
 +
 +===== Errata =====
 +
 +During final implementation work after the RFC was accepted, a number of cases were encountered which weren't explicitly specified in the original RFC text. They are documented here instead.
 +
 +==== Automatic promotion of arrays and objects ====
 +
 +PHP automatically initializes falsy values that are used as arrays or objects to an empty array or ''stdClass'' respectively. When this happens with a typed property or a reference to a typed property, the property type must be compatible with an array or stdClass object.
 +
 +<code php>
 +class Test {
 +    public ?int $prop = null;
 +}
 +
 +$test = new Test;
 +$test->prop[] = 123;       // TypeError, because we can't assign array to ?int
 +$test->prop->foobar = 123; // TypeError, because we can't assign stdClass to ?int
 +
 +$prop =& $test->prop;
 +$prop[] = 123;       // TypeError, because we can't assign array to ?int
 +$prop->foobar = 123; // TypeError, because we can't assign stdClass to ?int
 +</code>
 +
 +==== Strictness of runtime-evaluated default values ====
 +
 +Default values for both parameters and properties always follow the strict typing semantics, independently of the strict typing mode that applies in a particular file. However, there is one exception to this rule: If a constant expression parameter default value cannot be evaluated during compilation, it follows the strictness mode of the file instead:
 +
 +<code php>
 +function foo(int $x = FOO) { // currently allowed
 +    var_dump($x);
 +}
 +define('FOO', '42');
 +foo();
 +</code>
 +
 +For typed properties we do not make such an exception and following code will generate a TypeError:
 +
 +<code php>
 +class Test {
 +    public int $x = FOO; // TypeError
 +}
 +define('FOO', '42');
 +var_dump(new Test);
 +</code>
 +
 +The reason for this choice is that evaluation of constant expressions at compile-time vs run-time is an optimization choice and should not result in behavioral differences. Whether a constant expression is evaluated during compilation depends on many factors, including code order and whether or not opcache is enabled. We believe that the current behavior of parameters is a bug, not an intentional choice.
 +
 +==== Incrementing/decrementing beyond the maximal/minimal value ====
 +
 +When a value is incremented beyond ''PHP_INT_MAX'' or decremented beyond ''PHP_INT_MIN'' it is converted into a floating-point value and incremented/decremented as a floating-point value. Additionally, under PHPs type verification rules (both strict //and// weak), assigning an out-of-range floating point value to an integer is illegal.
 +
 +As stated, this would result in the following peculiar behavior: Incrementing an ''int'' property past the maximal value, would always be an error, because ''(float)PHP_INT_MAX + 1'' exceeds the integer range. However, decrementing an ''int'' property past the minimal value would only error on 32-bit systems. The reason is that on 64-bit systems ''(float)PHP_INT_MIN - 1'' is the same as ''(float)PHP_INT_MIN'', which is accurately representable as a double-precision floating point number and as such can be assigned back to an ''int'' property without error.
 +
 +As such, we would always generate an error on increment/decrement overflow, apart from the case of decrements on 64-bit systems.
 +
 +To avoid this, we instead define that incrementing/decrementing an ''int'' property past the maximal/minimal value always generated an error. It should be noted that this only affects the ''++'' and ''--'' operators. Overflows caused by other means are not handled specially.
  
 ===== Changelog ===== ===== Changelog =====
Line 1254: Line 1311:
 Significant changes to the RFC are noted here. Significant changes to the RFC are noted here.
  
 +  * 2019-01-07: Add errata: Increment/decrement overflow behavior.
 +  * 2019-01-03: Add errata: Strictness of runtime-evaluated default values.
 +  * 2019-01-03: Add errata: Automatic promotion of arrays and objects.
   * 2018-07-16: Add note about compatibility requirement on properties coming from traits.   * 2018-07-16: Add note about compatibility requirement on properties coming from traits.
   * 2018-07-10: Add shim header to make porting extension easy.   * 2018-07-10: Add shim header to make porting extension easy.
rfc/typed_properties_v2.txt · Last modified: 2019/01/11 16:16 by nikic