note 61744 added to language.references.spot

One may check reference to any object by simple operator==(
object). Example:

  class A {}

  $oA1 = new A();

  $roA = & $oA1;

  echo "roA and oA1 are " . ( $roA == $oA1 ?
"same" : "not same") .
"<br>";

  $oA2 = new A();
  $roA = & $roA2;

  echo "roA and oA1 are " . ( $roA == $oA1 ?
"same" : "not same") .
"<br>";

Output:

roA and oA1 are same
roA and oA1 are not same

Current technique might be useful for caching in objects
when inheritance is used and only base part of extended
class should be copied (analog of C++: oB = oA):

class A { 
  /* Any function changing state of A should set $bChanged
to true */
  public function isChanged() { return $this->bChanged; }
  private $bChanged;
  //...
}

class B extends A {
// ...
  public function set( &$roObj) {
    if( $roObj instanceof A) {
      if( $this->roAObj == $roObj &&
          $roObj->isChanged()) {
        /* Object was not changed do not need to copy A part
of B */
      } else {
        /* Copy A part of B */
        $this->roAObj = &$roObj;
      }
    }
  }

  private $roAObj;
}
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