Create a private Impl library

[jbdeboer]

Angular.dart should not be exporting internal classes to projects that import Angular.

One solution is to create a private Impl library which the main Angular.dart library imports.

[mhevery]

I am not convinced what is the best way to do this, and I am not a fan of SomeNameImpl classes.

[justinfagnani]

SomeNameImpl classes shouldn't really be common in Dart. First, you can just have a class and treat it as an interface, so you don't need the Foo/FooImpl split like in Java. Second, a private implementation can have the same name as the public class but with an underscore. Third, the "Impl" pattern was always a terrible idea, even in Java :) Those names should have described what the implementation actually did.

Depending on what you're trying to do there are a couple of approaches:

• Make more things private. Not many top-level names are private currently. Things like initWatchVal (unless it should be public) should be named _initWatchVal.
• Split Angular up into many libraries and only include in the top-level library (angular.dart) what applications need. Implementation libraries typically live in /lib/src. Their top-level names will be visible to the Angular libraries that import them, but not transitively visible to libraries that import Angular. On the Dart team we rarely use parts, and prefer libraries.
• If you have abstract class and concrete implementations and want to hide the implementations, make them private with a leading underscore.

Splitting up the libraries has side benefits. For instance, some of the code in Angular could be usable and testable outside of a browser if it was in a library that didn't import dart:html.

[mhevery]

+1 for making things private and for splitting into sub-libraries, still not sure how I feel about having interfaces and implementation.

[mhevery]

Split up angular to many smaller libraries.