PHP - define constant inside a class

Question

How can I define a constant inside a class, and make it so it's visible only when called in a class context?

....something like Foo::app()->MYCONSTANT;

(and if called like MYCONSTANT to be ignored)

Answer 1

See Class Constants:

class MyClass {     const MYCONSTANT = 'constant value';      function showConstant() {         echo  self::MYCONSTANT. "\n";     } }  echo MyClass::MYCONSTANT. "\n";  $classname = "MyClass"; echo $classname::MYCONSTANT. "\n"; // As of PHP 5.3.0  $class = new MyClass(); $class->showConstant();  echo $class::MYCONSTANT."\n"; // As of PHP 5.3.0 

In this case echoing MYCONSTANT by itself would raise a notice about an undefined constant and output the constant name converted to a string: "MYCONSTANT".

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EDIT - Perhaps what you're looking for is this static properties / variables:

class MyClass {     private static $staticVariable = null;      public static function showStaticVariable($value = null)     {         if ((is_null(self::$staticVariable) === true) && (isset($value) === true))         {             self::$staticVariable = $value;         }          return self::$staticVariable;     } }  MyClass::showStaticVariable(); // null MyClass::showStaticVariable('constant value'); // "constant value" MyClass::showStaticVariable('other constant value?'); // "constant value" MyClass::showStaticVariable(); // "constant value" 

Answer 2

This is and old question, but now on PHP 7.1 you can define constant visibility.

EXAMPLE

<?php class Foo {     // As of PHP 7.1.0     public const BAR = 'bar';     private const BAZ = 'baz'; } echo Foo::BAR . PHP_EOL; echo Foo::BAZ . PHP_EOL; ?> 

Output of the above example in PHP 7.1:

 bar  Fatal error: Uncaught Error: Cannot access private const Foo::BAZ in … 

Note: As of PHP 7.1.0 visibility modifiers are allowed for class constants.

More info here