Proposal for one-way binding option

[robstove]

I'd like to propose a way to allow directives to support one-way binding. Currently this is not an option and the only way to capture data from parent scope is by using two-way '=' binding or '&' binding. '&' binding would work but creates a semantic issue because it is expression based. To solve this a new binding option needs to be added so that we can do something like this:

scope: {
    myOneWayProperty: '-'
}

When the one-way binding option is specified this indicates that the scope property should be replaced with the evaluated value from $parent scope.

scope.myOneWayProperty = $parse(scope.myOneWayProperty)(scope.$parent);

With this option we can now pass objects to a directive without the need for two watches and without having function callback semantic

[Narretz]

Let's discuss this centralized here: #13854

[robstove]

Perfect thanks Martin!