在 PHP 类中是否可以在函数内部创建私有变量？

Question

在使用 PHP 类时，我注意到在类内部，当我以 $this->variablename 的方式将函数中的变量定义为该类的属性时，它会自动成为该类的公共变量。

class example {
    public function setstring() {
        $this->string = "string";
    }
}

这样

$class = new example();
echo $class->string; 

输出：string

但是，如果我想创建只能由类内的函数访问的私有变量，是否只能在 setstring() 函数内声明它们？而不是像这样在函数之外将它们声明为私有。

class example {
    private $string ='';
    public function setstring() {
        $this->string = "string";
    }
}

有人这样做的原因是为了整洁，以免在类开始时声明一长串私有变量。

Answer 1

不，没有办法做到这一点。

在 PHP 中，您通常使用自记录 cmets 按字母顺序在函数上方声明 all 您的类/实例属性。这是编写类的最“整洁”和清晰的方式。还建议您完全避免使用公共属性，根据需要使用 getter 和 setter。

PHP 的规范编码风格在PSR-1 和PSR-2 中定义。我还建议您查看PHPDoc。

请记住，在您的类方法范围内声明的变量将是该方法的私有变量。如果您打算从其他方法访问它，则只需要一个类属性。

<?php
class Example {

  /**
   * Holds a private string
   * @var string
   */
  private $string = '';

  /**
   * Sets the private string variable
   */
  public function setString() {
    $this->string = 'This string is accessible by other methods';
    $privateVar = 'This string is only accessible from within this method';
  }

}

Answer 2

如何使用 OOP 在 PHP 类中创建私有变量 （面向对象编程）。

在 PHP 类中声明私有变量的最佳方法是在 __Construction 方法上方创建它们，按照惯例，您可以在美元符号后使用下划线开始变量（即 $_private_variable），以让其他程序员阅读您的代码一看就知道是私有变量，brilliant！

请声明你在一个类中的所有变量都是私有的，除了总是公开的 __getter 和 __setter，除非你有理由不这样做。

使用 __setter (__set) 函数为类中的私有变量设置值，当需要该值时，使用 __getter (__get) 函数返回值。

为了理解它，让我们创建一个非常小的类，可用于创建不同类型的车辆，这将使您了解如何正确创建私有变量、为其设置值并从中返回值，准备好了吗？

    <?php

    Class Vehicle{

        /* Delcaration of private variables */

        private $_name = "Default Vehicle";
        private $_model;
        private $_type;
        private $_identification;

        /* Declaration of private arrays */
        private $_mode = array();
        private $feature = array();

        /* Magic code entry function, think of it as a main() in C/C++ */
        public function __construct( $name, $model, $type ){
            $this->create_vehicle( $name, $model, $type );
        }

        /* __getter function */
        public function __get( $variable ){
            if( !empty($this->$variable) ){
                $get_variable = $this->$variable;
            }

            return $get_variable;
        }

        /* __setter function */
        public function __set( $variable, $target ){
            $this->$variable = $target;
        }

        /* Private function */
        private function create_vehicle( $name, $model, $type ){
            $this->__set( "_name", $name );
            $this->__set( "_model", $model);
            $this->__set( "_type", $type );
        }

    }

    //end of the class.

?>

<?php
    /* Using the Vehicle class to create a vehicle by passing
       three parameters 'vehicle name', 'vehicle model', 'vehicle type' 
       to the class.
    */

    $toyota = new Vehicle("Toyotal 101", "TY101", "Sedan");

    /* Get the name and store it in a variable for later use */
    $vehicle_name = $toyota->__get('_name');

    /* Set the vehicle mode or status */
    $vehicle_mode = array(
            'gas' => 50,
            'ignition' => 'OFF',
            'tire' => "OK",
            'year' => 2020,
            'mfg' => 'Toyoda',
            'condition' => 'New'
        );

    /* Create vehicle features */    
    $vehicle_feature = array(
            "Tire" => 4,
            "Horse Power" => "V6",
            "blah blah" => "foo",
            "Airbag" => 2,
            "Transmission" => "Automatic"
            //....
        );

    /* Create vehicle identification */
    $vehicle_identification = array(
        "VIN" => "0001234567ABCD89",
        "NAME" => $vehicle_name,
        "FEATURE" => $vehicle_feature,
        "MODEL" => $vehicle_mode,
        "YEAR" => 2020,
        "MFG" => "Totota"
    ); 


    /* Set vehicle identification */
    $toyota->__set("_identification", $vehicle_identification );

    /* Set vehicle features */
    $toyota->__set("_feature", $vehicle_feature );

    /* Set vehicle mode */
    $toyota->__set("_mode", $vehicle_mode);

    /* Retrieve information and store them in variable using __get (getter) */
    $vehicle_name = $toyota->__get('_name');
    $vehicle_mode = $toyota->__get('_mode');
    $vehicle_id =  $toyota->__get('_identification');
    $vehicle_features = $toyota->__get('_feature');
    $vehicle_type = $toyota->__get('_type');
    $vehicle_model = $toyota->__get('_model');


    /* Printing information using store values in the variables. */
    echo "Printing Vehicle Information\n";
    echo "*****************************\n";

    echo "Vehicle name is $vehicle_name \n";
    echo "Vehicle Model is $vehicle_model \n";
    echo "Vehich type is $vehicle_type \n";

    printf("\n\n");
    echo "Printing Vehicle Mode\n";
    echo "***********************\n";
    print_r( $vehicle_mode );

    printf("\n\n");
    echo "Printing Vehicle Features\n";
    echo "**************************\n";
    print_r( $vehicle_features );

    printf("\n\n");

    echo "Printing Vehicle Identification\n";
    echo "******************************\n";
    print_r( $vehicle_id );


    printf("\n\n");
?>

这段代码的输出：

Printing Vehicle Information
*****************************
Vehicle name is Toyotal 101 
Vehicle Model is TY101 
Vehich type is Sedan 


Printing Vehicle Mode
***********************
Array
(
    [gas] => 50
    [ignition] => OFF
    [tire] => OK
    [year] => 2020
    [mfg] => Toyoda
    [condition] => New
)


Printing Vehicle Features
**************************
Array
(
    [Tire] => 4
    [Horse Power] => V6
    [blah blah] => foo
    [Airbag] => 2
    [Transmission] => Automatic
)


Printing Vehicle Identification
******************************
Array
(
    [VIN] => 0001234567ABCD89
    [NAME] => Toyotal 101
    [FEATURE] => Array
        (
            [Tire] => 4
            [Horse Power] => V6
            [blah blah] => foo
            [Airbag] => 2
            [Transmission] => Automatic
        )

    [MODEL] => Array
        (
            [gas] => 50
            [ignition] => OFF
            [tire] => OK
            [year] => 2020
            [mfg] => Toyoda
            [condition] => New
        )

    [YEAR] => 2020
    [MFG] => Totota
)

要使用此代码进行实时测试或试验，请参阅demo，更改名称，随意创建新车辆。

我希望这会有所帮助。

Answer 3

不可能作为语言功能，但有一个非常简单有效的技巧：

class Test
{
    /**
     * Hidden dynamic data.
     * @var object
     */
    private $_ = (object)[];

    public function setString()
    {
        $this->_->string = "string";
    }
}

您可以将$_ 更改为您想要的任何内容，但它对我来说确实看起来更老套。 $this->this 也是一个选项。