What does using a dollar sign after $this-> in PHP mean?

Question

I'm a little confused by some PHP syntax I've come across. Here is an example:

$k = $this->_tbl_key;

if( $this->$k)
{
   $ret = $this->_db->updateObject( $this->_tbl, $this, $this->_tbl_key, $updateNulls );
}
else
{
    $ret = $this->_db->insertObject( $this->_tbl, $this, $this->_tbl_key );
}

My question is basically what does $this->$k mean? I figured it might mean the member variable that goes by the name of whatever is in $this->_tbl_key, but how would that work? Is it possible to add member variables to a class at run-time?

Answer 1

It'll look up whatever the value of "k" is, and treat it as a variable name. These two samples are the same:

echo ($obj->myvar);

####

$k = "myvar";
echo ($obj->$k);

Answer 2

I believe that is a case of variable variables.

Answer 3

no it's not