php中的 类常量 Class Constants
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. Like static members, constant values cannot be accessed from an instance of the object (using $object::constant).
说明： const 常量 不用 $ 符号
const 不加关键字 private 修饰 //Like static members,
不能通过 对象访问。 只能通过class访问
例子 19-15. Defining and using a constant
<?php
class MyClass
{
const constant = 'constant value';
function showConstant() {
echoself::constant . "/n";
}
}
echo MyClass::constant . "/n";
$class = new MyClass();
$class->showConstant();
// echo $class::constant;is not allowed
?>
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