php class constants

You can define values ​​that remain unchanged in the class as constants. There is no need to use the $ symbol when defining and using constants.

The value of a constant must be a fixed value and cannot be a variable, class attribute, the result of a mathematical operation or a function call.

Constants can also be defined in interfaces.

Since PHP 5.3.0, you can use a variable to dynamically call a class. But the variable value cannot be a keyword (such as self, parent or static).

Example #1 Define and use a class constant

class MyClass
{    const constant = 1;
    function showConstant(){
        echo self::constant.&#39;<br>&#39;;
    }
}
echo MyClass::constant.&#39;<br>&#39;;
$className = "MyClass";
echo $className::constant.&#39;<br>&#39;; //自PHP5.3.0起
$class = new MyClass();
$class -> showConstant();
echo $class::constant.&#39;<br>&#39;;

Example #2 Static data example

class foo{
    const bar = <<<&#39;EOT&#39;
        bar
EOT;
}

Unlike heredoc, nowdoc can be used in any static data.