How do I assign a getter/setter function pair in TypeScript?

Question

I'm using TypeScript with Angular. I'm interested in adding to the scope of a controller a pair of functions, currentPath(): string and currentPath(newValue: string): void, and forbid direct access to the backing variable. I also wanted to factor out this “property-like” behaviour. So I added an interface:

interface Property<T> {
    (): T;
    (newValue: T): void;
}

And then tried to configure my scope like this:

interface ApplicationRootScope extends ng.IScope {
    currentPath: Property<string>;
}

appControllers.controller('MyCtrl', ($scope: ApplicationRootScope) => {
    var _currentPath = "n/a";
    $scope.currentPath = { // this assignment fails
        (): string = _currentPath;
        (newValue: string) => {
            _currentPath = newValue;
        }
    };
});

The assignment at the marked line fails — I'm using wrong syntax on purpose to demonstrate what I'd like to do. Is there any way for me to assign the currentPath variable directly like this?

Answer 1

Function overloading is only a type system feature; JavaScript/TypeScript does not directly support overloading on function arity.

What you want to write is this:

$scope.currentPath = function(arg?: string) {
    if(arguments.length === 0) {
        return _currentPath;
    } else {
        return _currentPath = arg;
    }
}