Testing if property exists

Question

I read on php docs that isset is faster than property_exists and we should use a combination of both like

if (isset($this->$fld) || property_exists($this, $fld)) { 

But why can't I just use isset then?

if (isset($this->$fld)) {

Answer 1

Because property_exists will tell you if its even a defined property of the class/object where as isset doesnt make that distinction. for example:

class A {
  protected $hello;
}

class B {

}

using property_exists($this, 'hello') in class a will return true, while using it in class B will return false. isset will return false in both instances.

Answer 2

It depends on how your program is done, but if you read the comments in the manual it will help with explaining idiosyncrasies of a function.

http://php.timesoft.cc/manual/en/function.property-exists.php

The important part is here:

The documentation leaves out the important case of new properties you add to objects at run time. In fact, property_exists will return true if you ask it about such properties.