php - Assigning a function to a property of a class

I'm trying to do something similar to PHP anonymous function assigned to class property in constructor is always null?, but my solution seems more simple. I wanted comments from the Stack Overflow Hot Shots on this solution and whether there is a better one. This is kind of a 'best practices' question.

I want to pass a function (anonymous or defined) to a class/object and be able to call that function later. I started with this :

function Foo($arg) {return sprintf('In Foo(%s)',$arg);}
function Bar($arg) {return sprintf('In Bar(%s)',$arg);}

class TestIt {
  private $func;

  public function __construct( $func ) { $this->func = $func; }

  public function OutPut($arg) {
    return $this->func($arg);
  }
}

$test  = new TestIt('Foo');
echo $test->OutPut('Bozo');
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When this is run, I get an error that the method$this->func doesn't exist. If I put ais_callable test inside the methodOutPut(), I find the$this->func is, in fact, callable, but the error persists.

However, if I us the third argument ofis_callable, I get this to work fine.

public function OutPut($arg) {
  return is_callable($this->func,false,$tmpfunc) ? $tmpfunc($arg) : null;
}
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How does this stack up as a solution? Curious of your thoughts.