回应PHP类属性

Question

can somebody explain to me why the property $message is null before the method 'getMessage'?

I was expecting it to return 'this is a message' but it returns null, it only returns a string once I reset it in the method.

Cheers

<?php

class Data {
    public $message = 'this is a message';

    public function getMessage() {
        return $this->$message = 'new value';
    }
}

$object = new Data;

var_dump($object->$getMessage); // Equals Null

echo $object->getMessage(); // Equals 'New value'

Answer 1

There is no variable $getMessage defined, yet you're trying to use it as though it was a property name; so of course it can't return anything

If you assigned a value to $getMessage, e.g.

$getMessage = 'message';

then using

$object->$getMessage

will treat this as $object->message (like a variable variable) to point to the message property

---

Then in your getMessage() method, you have

return $this->$message = 'new value';

which will use the value of the variable $message (which isn't defined) and use it like a variable variable again to set a property named by that (non-existent) value.

---

To reference the message properties in the class, it's $this->message, not $this->$message