Class constants store fixed values on a type and can use public, protected or private visibility.
The examples below begin with the core behavior, then move to an application-oriented use.
How PHP Class Constants and Visibility Works
Class constants store fixed values on a type and can use public, protected or private visibility.
Example 1: Basic Usage
This example uses a small input to make the main behavior visible.
<?php
class HttpStatus { public const int OK = 200; private const int INTERNAL = 999; }
echo HttpStatus::OK;Output:
200Class constants store fixed values on a type and can use public, protected or private visibility.
Example 2: A Different Input
A different set of values shows the same operation in another situation.
<?php
class FeatureFlag { protected const bool ENABLED = true; public static function enabled(): bool { return self::ENABLED; } }
var_dump(FeatureFlag::enabled());Output:
bool(true)Do not confuse class constants with instance properties; access control applies to constants too.
Practical Example: Applying the Feature
This example shows an application-style use of the feature, with its surrounding setup visible.
<?php
class SecurityPolicy { public const string DEFAULT_ROLE = "reader"; private const int ATTEMPTS = 3; public static function attempts(): int { return self::ATTEMPTS; } }
echo SecurityPolicy::DEFAULT_ROLE . ":" . SecurityPolicy::attempts();Output:
reader:3The code is shown for learning. Adjust the class names, inputs and error handling to suit your application.
Important Behavior and Edge Cases
- Do not confuse class constants with instance properties; access control applies to constants too.
- Class constants store fixed values on a type and can use public, protected or private visibility.
- Observe differences in empty inputs, invalid states and optional extension availability where relevant.
Comparison With Related Approaches
| Approach | Important Difference |
|---|---|
PHP Class Constants and Visibility | Class constants store fixed values on a type and can use public, protected or private visibility. |
| Alternative approach | Enums are preferable when modeling a closed set of related named states. |
Common Beginner Mistakes
| Mistake | Correct Approach |
|---|---|
Ignoring the documented state or precondition of PHP Class Constants and Visibility | Do not confuse class constants with instance properties; access control applies to constants too. |
| Expecting a different type of result | Read the declared return type and distinguish returned values from changes to the source object. |
| Assuming a related API works identically | Enums are preferable when modeling a closed set of related named states. |
Key Takeaways
- Class constants store fixed values on a type and can use public, protected or private visibility.
- Do not confuse class constants with instance properties; access control applies to constants too.
- Use the example that matches the values, runtime version and dependencies in your application.
PHP Class Constants and Visibility is useful when its behavior matches the data structure and lifecycle of your PHP application. Choose it with a clear understanding of its preconditions and returned values.