Type hinting for arrays with string key

Is it possible to hint at the types for an array when it has a key? For example

class Table{
     //Stores information about SQL tables
}

function testFunction(){

     $tables = array();

     $tables['comments'] = new Table();

     $tables['users'] = new Table();

     testFunction2($tables);

}

/**

*  @param $tables <-- what goes here?

*/

function testFunction2($tables){

    foreach($tables as $index => $table){

    }

}

Please can you tell me what I should put to hint that $index is a string and $table is a Table.

Apologies if this has been asked many times before but I couldn't see an answer.