Common magic method functions and usage in PHP

This article mainly introduces the functions and usage of common magic methods in PHP. It has certain reference value. Now I share it with everyone. Friends in need can refer to it

Overview

In object-oriented programming, PHP provides a series of magic methods, which provide a lot of convenience for programming. Magic methods in PHP usually start with __ (two underscores) and do not require explicit calls but are triggered by certain conditions.

Before starting

Before summarizing PHP’s magic methods, let’s define two classes for use in later examples:

<?php
class Device{    
public $name,$battery,$data = [],$connection;    
protected function connect(){        
$this->connection = &#39;resource&#39;;        
echo $this->name.&#39;connected&#39;.PHP_EOL;
    }    
    protected function disconnect(){       
    $this->connection = null;        
    echo $this->name.&#39;disconnected&#39;.PHP_EOL;
    }
}

The Device class has four member attributes and two member methods.

<?php 

class Battery{    
private $charge = 0;    
public function setCharge($charge){        
$charge = (int)$charge;        
if($charge < 0){            
$charge = 0;
        }else if($charge > 100){            
        $charge = 100;
        }        $this->charge = $charge;
    }
}

The Battery class has one member property and one member method.

Constructor and destructor

Constructor and destructor are called when the object is created and destroyed respectively. When an object is "destroyed", it means that there is no reference to the object. For example, if the variable that refers to the object is deleted (unset), reassigned, or the script execution ends, the destructor will be called.

__construct()

__construct()The constructor is by far the most commonly used function. When creating an object, you can do some initialization work in the constructor. You can define any number of parameters for the constructor, as long as the corresponding number of parameters is passed in when instantiating. Any exception that occurs in the constructor prevents the object from being created.

<?php
class Device{    
public $name,$battery,$data = [],$connection;    
public function __construct(Battery $battery,$name){        
$this->battery = $battery;        
$this->name = $name;        
$this->connect();
    }    protected function connect(){        
    $this->connection = &#39;resource&#39;;        
    echo $this->name.&#39;connected&#39;.PHP_EOL;
    }    protected function disconnect(){        
    $this->connection = null;        
    echo $this->name.&#39;disconnected&#39;.PHP_EOL;
    }
}

In the above sample code, the constructor of the Device class assigns values ​​to the member properties and calls the connect() method.

Declaring the constructor as a private method prevents objects from being created outside the class, which is often used in the simplex pattern.

__desctruct()

The destructor is usually called when the object is destroyed. The destructor does not receive any parameters. Some cleanup work is often performed in the destructor, such as closing the database connection, etc.

__get()

The magic method __get() is called when we try to access a property that does not exist. It receives a parameter that represents the name of the accessed attribute and returns the value of the attribute. In the Device class above, there is a data attribute, which plays a role here, as shown in the following code:

<?php 

class Device{    
public $name,$battery,$data = [],$connection;    
public function __construct(Battery $battery,$name){        
$this->battery = $battery;        
$this->name = $name;        
$this->connect();
    }    protected function connect(){        
    $this->connection = &#39;resource&#39;;        
    echo $this->name.&#39;connected&#39;.PHP_EOL;
    }    
    protected function disconnect(){        
    $this->connection = null;        
    echo $this->name.&#39;disconnected&#39;.PHP_EOL;
    }
}
$battery = new Battery();
$device = new Device($battery,&#39;mac&#39;);
echo $device->aaa; //Notice: Undefined property: Device::$aaa

<?phpheader("Content-type: text/html; 
charset=utf-8");
class Device{    
public $name,$battery,$data = [],$connection;   
public function __construct(Battery $battery,$name){        
$this->battery = $battery;        
$this->name = $name;        
$this->connect();
    }    
    public function __get($name){        
    if(array_key_exists($name,$this->data)){            
    return $this->data[$name];
        }        
        return &#39;属性不存在&#39;;
    }    
    protected function connect(){        
    $this->connection = &#39;resource&#39;;        
    echo $this->name.&#39;connected&#39;.PHP_EOL;
    }    protected function disconnect(){        
    $this->connection = null;        
    echo $this->name.&#39;disconnected&#39;.PHP_EOL;
    }
}$battery = new Battery();
$device = new Device($battery,&#39;mac&#39;);
echo $device->aaa; //macconnected 属性不存在

The most commonly used place for this magic method is to create a "read-only" Properties to extend access control. In the above Battery class, there is a private property $charge, which we can extend through the __get() magic method to be readable but not modifyable outside the class. The code is as follows:

<?php 

class Battery {    
private $charge = 0; 
    public function  __get($name) {        
    if(isset($this->$name)) {            
    return $this->$name;
        }        
        return null;
    }
}

__set()

__set() magic method will be called when we try to modify an inaccessible property. It receives two parameters, One represents the name of the attribute, and one represents the value of the attribute. The sample code is as follows:

<?php
header("Content-type: text/html; charset=utf-8");
class Device{    
public $name,$battery,$data = [],$connection;    
public function __construct(Battery $battery,$name){        
$this->battery = $battery;        
$this->name = $name;       
$this->connect();
    }    
    public function __get($name){        
    if(array_key_exists($name,$this->data)){            
    return $this->data[$name];
        }        
        return &#39;属性不存在&#39;;
    }    
    public function __set($name,$value){        
    $this->data[$name] = $value;
    }    protected function connect(){        
    $this->connection = &#39;resource&#39;;        
    echo $this->name.&#39;connected&#39;.PHP_EOL;
    }    protected function disconnect(){        
    $this->connection = null;        
    echo $this->name.&#39;disconnected&#39;.PHP_EOL;
    }
}$battery = new Battery();
$device = new Device($battery,&#39;mac&#39;);
$device->aaa = &#39;哈哈&#39;;
echo $device->aaa; //macconnected 哈哈

__isset()

__isset() magic method will be called when the isset() method is called on an inaccessible property. It receives A parameter indicating the name of the attribute. It should return a Boolean value indicating whether the property exists. The code is as follows:

<?php
class Device{    
private function __isset($name){        
return array_key_exists($name,$this->data);
    }

If the members in the object are public, you can use the isset() function directly. If it is a private member attribute, you need to add an __isset() method to the class

__unset()

__unset() magic method before calling unset The () function is called when destroying an inaccessible property. It receives a parameter expressing the name of the property.

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Introduction to PHP’s magic constants (variables), magic methods (functions), and superglobal variables

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