some questions about store datas on variable in class on php8

I don’t know if I do something wrong, please help solve this problem

when I tried to use variable in class to store data just like

class Send
{
    private $_email;
    
    public function sendMail()
    {
        $this->_email->to = 'xxx';
        
        $this->do();
    }

    public function do()
    {
        // code    
    }
}

in the function sendMail() I tried to use $this->_email->to to store user’s mail, and in function do() to read it, but some error occurred, it tells me that Attempt to assign property "to" on null

and I remember it will be work in php 7.x

>Solution :

In PHP you can just assign values to a variable of a simple datatype like string or integer, but this is not true for objects.

Objects need to be instantiated first, using the new keyword.

public function sendMail()
{
    $this->_email = new Email();
    $this->_email->to = 'xxx';
    $this->_email->sendMail();
}

The class Email of course has to be defined first. It can have properties and methods for all of your needs.