The PHP subclass overrides the parent class value?

    class A extends B {    public function __construct($config) {        foreach ($config as $k => $v) {            echo $k;            var_dump(isset($this->$k));            if (isset($this->$k)) {                $this->$k = $v;            }        }        exit;class B {    public $appid;    public $templateId;    public $api;    public $accountSid;    public $token;    public $version;

Results of printing
Appidbool (False)
Templateidbool (False)
Apibool (False)
Accountsidbool (False)
Tokenbool (False)
Versionbool (False)

Isset ($this-$k) Why is False

Reply content:

    class A extends B {    public function __construct($config) {        foreach ($config as $k => $v) {            echo $k;            var_dump(isset($this->$k));            if (isset($this->$k)) {                $this->$k = $v;            }        }        exit;class B {    public $appid;    public $templateId;    public $api;    public $accountSid;    public $token;    public $version;

Results of printing
Appidbool (False)
Templateidbool (False)
Apibool (False)
Accountsidbool (False)
Tokenbool (False)
Versionbool (False)

Isset ($this-$k) Why is False

Use Isset () to determine whether a nonexistent value or a variable with a value of NULL will return FALSE.
In base class B, only variables such as AppID are declared, and no specific values are assigned.

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