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RFC: Static class #14861

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RFC: Static class #14861

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@Bilge Bilge commented Jul 7, 2024 •
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This implements static classes as described in the RFC and supersedes #14583. Static classes are implemented with the following semantics:

  • Cannot be instantiated by any mechanism.
    • Cannot be instantiated with the new keyword.
    • Cannot be instantiated with unserialize().
    • Cannot be instantiated via reflection (e.g. new ReflectionClass()->newInstance()).
  • Mutually exclusive with the readonly modifier.
  • Cannot be applied to anonymous classes.
  • Supports inheritance, but only if the super/subclass is also marked static.
  • Supports abstract static classes.
  • Supports traits, but only if all their properties and methods are static.
  • Adds ReflectionClass::isStatic().

Thanks

  • Thanks to @sj-i and @iluuu1994 for implementation assistance.
  • Thanks to @oplanre for the initial implementation prototype.

@Bilge Bilge force-pushed the feature/static-class branch from e7a74bc to 15539e0 Compare July 7, 2024 15:11
@Bilge Bilge marked this pull request as ready for review July 7, 2024 15:27
@Bilge Bilge changed the title Added static classes RFC: Static class Jul 7, 2024
iluuu1994
iluuu1994 reviewed Jul 8, 2024
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I'm not particularly in favor of this change, but the code mostly LGTM!

Zend/zend_API.c
@@ -1795,13 +1795,15 @@ ZEND_API void object_properties_load(zend_object *object, HashTable *properties)
* calling zend_merge_properties(). */
static zend_always_inline zend_result _object_and_properties_init(zval *arg, zend_class_entry *class_type, HashTable *properties) /* {{{ */
{
if (UNEXPECTED(class_type->ce_flags & (ZEND_ACC_INTERFACE|ZEND_ACC_TRAIT|ZEND_ACC_IMPLICIT_ABSTRACT_CLASS|ZEND_ACC_EXPLICIT_ABSTRACT_CLASS|ZEND_ACC_ENUM))) {
if (UNEXPECTED(class_type->ce_flags & (ZEND_ACC_STATIC|ZEND_ACC_INTERFACE|ZEND_ACC_TRAIT|ZEND_ACC_IMPLICIT_ABSTRACT_CLASS|ZEND_ACC_EXPLICIT_ABSTRACT_CLASS|ZEND_ACC_ENUM))) {
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This is repeated often enough to where it probably makes sense to extract it into a new macro. E.g. ZEND_ACC_UNINSTANTIABLE_FLAGS.

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Would you perhaps agree this is best left for a separate refactoring PR?

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Bilge commented Jul 8, 2024

@iluuu1994 Thanks so much for the (thorough) review!

About half the comments pertain to @oplanre's changes, so I am unable to comment on why they were made, but nevertheless I take ownership of them now, so I will make the requested changes.

Is it acceptable to rebase so changes not wanted can be as if they were never made, or should I add additional commits to revert where required?

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@Bilge Whichever you prefer. Commits can help for large PRs, but rebasing in this case seems fine.

@Bilge Bilge force-pushed the feature/static-class branch 2 times, most recently from caa6595 to ed7852b Compare July 8, 2024 21:02
oplanre and others added 4 commits July 8, 2024 22:06
@oplanre @Bilge
Implement static classes
8b13efc
@Bilge
Added tests for static class feature.
3ed2d03 
Added compile-time check to enforce all methods must be declared static in a static class.
Added compile-time mutual-exclusivity check for static classes marked with abstract or readonly modifiers.
Added compile-time check to preclude static class inheriting from non-static class and vice-versa.
Added compile-time check to preclude static class using a trait with non-static properties or methods.
Fixed ZEND_ACC_IMPLICIT_ABSTRACT_CLASS collision with ZEND_ACC_STATIC.
@Bilge
Added ReflectionClass::isStatic and accompanying test.
b6d0a30
@Bilge
Fix "readonly" tests relying on specific Bison output.
f6916fe 
Fix reflection test.
@Bilge Bilge force-pushed the feature/static-class branch 2 times, most recently from aaa7c9a to 4c0d0d6 Compare July 9, 2024 21:25
@Bilge
Removed mutual modifier restriction for abstract static class.
23d0272 
Improved a couple of static class tests per feedback.
@Bilge Bilge force-pushed the feature/static-class branch from 4c0d0d6 to 23d0272 Compare July 9, 2024 21:28
@Bilge Bilge requested a review from iluuu1994 July 9, 2024 21:52
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@Bilge @iluuu1994 @oplanre