Class Constants

Examples:

Defining and using a constant

It is possible to define constant values on a per-class basis remaining the same and unchangeable. Constants differ from normal variables in that you don't use the $ symbol to declare or use them.

The value must be a constant expression, not (for example) a variable, a property, or a function call.

It's also possible for interfaces to have constants. Look at the interface documentation for examples.

As of PHP 5.3.0, it's possible to reference the class using a variable. The variable's value can not be a keyword (e.g. self, parent and static).

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

Static data example

<?php
class foo {
    // As of PHP 5.3.0
    const BAR = <<<'EOT'
bar
EOT;
    // As of PHP 5.3.0
    const BAZ = <<<EOT
baz
EOT;
}
?>

Constant expression example

Note:

Support for initializing constants with Heredoc and Nowdoc syntax was added in PHP 5.3.0.

<?php
const ONE = 1;
 
class foo {
    // As of PHP 5.6.0
    const TWO = ONE * 2;
    const THREE = ONE + self::TWO;
    const SENTENCE = 'The value of THREE is '.self::THREE;
}
?>

It is possible to provide a scalar expression involving numeric and string literals and/or constants in context of a class constant.

Links:

http://php.net/manual/en/language.oop5.constants.php

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2025-01-10 15:47:30

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