PHP Common Concepts Confuse (v) the difference between PHP class constants, static properties, and attributes

In the recent reading of the handbook, I found that PHP has a number of pits, a note will fall in, while looking at the content of these easy to confuse the record down.

Tips: It's best to look at the manual in English, because there are a number of things in the English manual that are not available in the Chinese manual (latest PHP)

1. PHP5.3 supports calling classes with a variable
2. PHP5.6 supports assigning values with an expression PHP类常量 andPHP静态属性
3. PHP7.1 support for PHP类常量 increased access control

Brief introduction

• PHP class constants: defined in the same way as constants
• PHP Properties: Define the same way as variables
• PHP static properties: can be defined as PHP properties, add a static

PHP Properties

• Using -> the accessed variable
• Subclasses can override variables of the parent class
• Variables can be modified at any time
• Using Access in a class $this

PHP class Constants

• With :: access class constants, you can pass 类 and 对象 get class constants.

    <?php  class test{      const AAAA = "BBB";  }  $test = new test;  echo test::AAAA;  //BBB  echo $test::AAAA;   //BBB

• Subclasses can override the class constants of the parent class

    <?php  class test{      const AAAA = "BBB";  }  class test2 extends test{      const AAAA = "ccc";      public function gettest(){          return parent::AAAA;      }  }     $test = new test2;  echo test::AAAA;   //ccc  echo test2::AAAA;  //ccc  echo $test::AAAA;  //BBB  echo $test->gettest();  //BBB

• Once a class constant is defined, it cannot be modified

• Using Access in a class self::类常量

PHP Static Properties

• Using :: access static properties, you can pass 类 and 对象 get static properties.

   <?php class test{     public static $AAAA = "BBB"; } $test = new test; echo test::$AAAA;    //BBB echo $test::$AAAA;   //BBB

• Subclasses can override static properties of the parent class

    <?php  class test{      public static $AAAA = "BBB";  }  class test2 extends test{      public static $AAAA = "CCC";  }  $test = new test2;  echo test2::$AAAA;   //CCC  echo $test::$AAAA;   //CCC

• Class constants define the modifications that can be made at any time

• Re-use in class self::$test to access

PHP Common Concepts Confuse (v) the difference between PHP class constants, static properties, and attributes