What is the access syntax for PHP object properties?

Question

How to access the properties of a PHP object?

Also, what is the difference between accessing object properties using $this->$property1 and $this->property1?

When I try to use $this->$property1 I get the following error:

'PHP: Cannot access null property'.

There is a comment in PHP's object properties documentation that mentions this problem, but the comment does not explain it in detail.

Answer 1

$this->property1 means:

Use the object and get the variables bound to the object property1

$this->$property1 means:

Evaluate the string $property1 and use the result to obtain a variable named by the $property1 result, which is bound to the object

Answer 2

1. $property1 //Specific variable
2. $this->property1 //Specific property

In the normal usage of the class, there is no need to use "$", otherwise you will call a variable named $property1, which can take any value.

Example:

class X {
  public $property1 = 'Value 1';
  public $property2 = 'Value 2';
}
$property1 = 'property2';  // 属性2的名称
$x_object = new X();
echo $x_object->property1; // 返回 'Value 1'
echo $x_object->$property1; // 返回 'Value 2'