Fetch object data from string stored in variable

Question

When object name ( category ) put directly it returns correct value Like:

 $primary = $this->dbmapper->category['primary'] ;  // ( Correct Output )

But when , put object name in a variable called $dataname, it returns blank, like:

 $dataname = 'category';
 $primary = $this->dbmapper->$dataname['primary'] ;   ( Blank Output )

my constructor variable is:

  $this->dbmapper = $this->mapper();

My function is:

  function mapper($module='')
    {
        $mapper =  array();
        $mapper['category']['table'] = 'allcategory';
        $mapper['category']['primary'] = 'categoryID';
        $mapper['page']['table'] = 'allpages';
        $mapper['page']['primary'] = 'pageID';
        return (object) $mapper;
    }

Answer 1

To access an object property(especially if it's an array) via variable enclose it with braces:

...
$dataname = 'category';
$primary = $this->dbmapper->{$dataname}['primary'];