php定义类常量

class MyClass {
    const CONSTANT_NAME = 'value';
}

class MathConstants {
    const PI = 3.14159;
    const E = 2.71828;
}

echo MathConstants::PI; // 输出: 3.14159
echo MathConstants::E;  // 输出: 2.71828

class MyClass {
    const CONSTANT_NAME = 'value';
}

// 错误的尝试修改类常量
MyClass::CONSTANT_NAME = 'new value'; // 这将导致致命错误

namespace MyNamespace;

class MyClass {
    const CONSTANT_NAME = 'value';
}

namespace AnotherNamespace;

class AnotherClass {
    const CONSTANT_NAME = 'another value';
}

echo MyNamespace\MyClass::CONSTANT_NAME; // 输出: value
echo AnotherNamespace\AnotherClass::CONSTANT_NAME; // 输出: another value