For example, in a directive:

...
scope: {
  cb: "&"
}
...

And in the template, passing in a function reference:

<foo cb="cbParent" />

In the directive I would need to call the function cb twice like so $scope.cb()() in order to really execute the function in the parent scope, because it's coming wrapped in another function.

My question is, why does angular wrap the function in another function?