Testing if property exists

I read on php docs that isset() is faster than property_exists() and we should use a combination of both 开发者_运维技巧like

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

But why can't I just use isset then?

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

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.

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.net/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.