PHP 8.3 introduced several small features that look minor, but one of the most powerful is typed class constants. Most developers ignore them, yet they solve real problems in large codebases.
Before PHP 8.3, class constants had no type. You could document them with PHPDoc, but PHP would not enforce anything. This caused silent bugs when constants were overridden or refactored incorrectly.
class Status {
public const ACTIVE = 1;
}
Nothing prevented this later:
class ExtendedStatus extends Status {
public const ACTIVE = "yes"; // silently allowed before
}
This breaks logic in subtle ways and is hard to detect.
PHP 8.3 allows you to declare a type for class constants, and PHP will enforce it at runtime.
class Status {
public const int ACTIVE = 1;
public const int INACTIVE = 0;
}
Now this becomes a fatal error:
class ExtendedStatus extends Status {
public const string ACTIVE = "yes"; //
Type error
}
This is not just syntactic sugar:
Typed constants give the engine stronger guarantees about values. This allows better optimizations in opcode generation and reduces defensive checks in critical paths.
Typed class constants are a small feature with a big impact. They increase correctness, improve maintainability, and quietly help performance. This is the kind of change that makes PHP 8.x feel more like a modern systems language.
The Problem: Untyped Constants Are Unsafe
Before PHP 8.3, class constants had no type. You could document them with PHPDoc, but PHP would not enforce anything. This caused silent bugs when constants were overridden or refactored incorrectly.
class Status {
public const ACTIVE = 1;
}
Nothing prevented this later:
class ExtendedStatus extends Status {
public const ACTIVE = "yes"; // silently allowed before
}
This breaks logic in subtle ways and is hard to detect.
The PHP 8.3 Solution: Typed Class Constants
PHP 8.3 allows you to declare a type for class constants, and PHP will enforce it at runtime.
class Status {
public const int ACTIVE = 1;
public const int INACTIVE = 0;
}
Now this becomes a fatal error:
class ExtendedStatus extends Status {
public const string ACTIVE = "yes"; //
Type error}
Why This Actually Helps
This is not just syntactic sugar:
- Prevents invalid overrides in inheritance
- Makes refactoring safer in large systems
- Improves static analysis accuracy
- Reduces production bugs caused by wrong constant values
Performance Side Effect (Hidden Benefit)
Typed constants give the engine stronger guarantees about values. This allows better optimizations in opcode generation and reduces defensive checks in critical paths.
Where This Matters Most
- Domain models
- Enums replacements
- Configuration constants
- Framework core code
Conclusion
Typed class constants are a small feature with a big impact. They increase correctness, improve maintainability, and quietly help performance. This is the kind of change that makes PHP 8.x feel more like a modern systems language.