Usage of => and -> and :: in PHP

Recommended manual:php complete self-study manual

1. Usage of =>

Array default key in php The name is an integer, you can also define any character key name yourself (preferably with practical meaning), such as:

　$css=array('style'=>'0'，‘color’=>‘green‘)；
　　则$css['style']=='0'，$css['color']=='green'。

2, usage of ->

-> is used to reference objects Members (properties and methods);

  <?php 
    $arr=[&#39;a&#39;=>123,&#39;b&#39;=>456];//数组初始化 
    echo $arr[&#39;a&#39;];//数组引用 
    print_r($arr);//查看数组 
    class A{ 
      public $a=123; 
      public $b=456; 
    } 
    $obj=new A();
    echo $obj->a;//对象引用
    print_r($obj);//查看对象
  ?>

Output results:

123Array(
    [a] => 123
    [b] => 456)
123A Object(
    [a] => 123
    [b] => 456)

3. Usage of ::

Double colon operator is the scope limitation operator Scope Resolution Operator You can access static, const, and overridden properties and methods in classes.

(1) Program List: Use variables to access outside the class definition

  <?php 
  class Fruit { 
      const CONST_VALUE = &#39;Fruit Color&#39;; 
  } 
   
  $classname = &#39;Fruit&#39;; 
  echo $classname::CONST_VALUE; // As of PHP 5.3.0 
   
  echo Fruit::CONST_VALUE;
  ?>

(2) Program List: Use outside the class definition::

    
  <?php 
  class Fruit { 
      const CONST_VALUE = &#39;Fruit Color&#39;; 
  } 
   
  class Apple extends Fruit 
  { 
      public static $color = &#39;Red&#39;;
  
      public static function doubleColon() {
          echo parent::CONST_VALUE . "\n";
          echo self::$color . "\n";
      }
  }
  
  Apple::doubleColon();
  ?>

(3) Program List: Call the parent method

  <?php 
  class Fruit 
  { 
      protected function showColor() { 
          echo "Fruit::showColor()\n"; 
      } 
  } 
   
  class Apple extends Fruit
  {
      // Override parent&#39;s definition
      public function showColor()
      {
          // But still call the parent function
          parent::showColor();
          echo "Apple::showColor()\n";
      }
  }
  
  $apple = new Apple();
  $apple->showColor();
  ?>

(4) Program List: Use the scope qualifier

     
  <?php 
      class Apple 
      { 
          public function showColor() 
          { 
              return $this->color; 
          } 
      }
  
      class Banana12     {
          public $color;
  
          public function __construct()
          {
              $this->color = "Banana is yellow";
          }
  
          public function GetColor()
          {
              return Apple::showColor();
          }
      }
  
      $banana = new Banana;
      echo $banana->GetColor();
  ?>

(5) Program List: Call the base class method

       
  <?php 
   
  class Fruit 
  { 
      static function color() 
      { 
         return "color"; 
      }
  
      static function showColor()
      {
          echo "show " . self::color();
      }
  }
  
  class Apple extends Fruit
  {
      static function color()
      {
          return "red";
      }
  }
  
  Apple::showColor();
  // output is "show color"!
  
  ?>

Related article recommendations:
1.Introduction to the meaning of the double colon::range parsing operator in php
2.The difference between the double colon range parsing operator and the arrow-> operator in php
Related video recommendations:
1.Dugu Jiujian (4)_PHP video tutorial
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