匿名函数作为命名空间之间的参数传递

The following code causes PHP to throw an error:

namespace NamespaceOne;

class MyClass {
    function __construct( array $config ) {
        $func = $config['func'];
        $value = 'Hello World';
        echo $func( $value );   // This part throws the error
    }
}

The class is instantiated in a different file:

namespace NamespaceTwo;

$class = new \NamespaceOne\MyClass( array(
    'func' => function( $v ) { return $v; }
));

Terminates with the error:

Fatal error: Function name must be a string [...]

EDIT

If I re-declare the function inside the namespace, it works:

class MyClass {
    function __construct( array $config ) {
        $config['func'] = function( $v ) { return $v; };
        $func = $config['func'];
        $value = 'Hello World';
        echo $func( $value );   // Echos "Hello World"
    }
}

So now we know what causes it to break, but how do we pass an anonymous function between namespaces?

namespace MyNamespace {

class MyClass {

    function __construct(array $config) {
        $func = $config['func'];
        $value = 'Hello World';
        echo $func($value);   // This part throws the error
    }

}

}