This example illustrates how a GUI framework can organize its classes into independent libraries:
The gui library defines interfaces for all the components.
It has no external dependencies.
The windows-gui library provides Windows implementation of the base GUI.
Depends on gui.
The macos-gui library provides Mac OS implementation of the base GUI.
Depends on gui.
The app is a client application that can use several implementations of the GUI framework, depending on the current environment or configuration. However, most of the app code doesn't depend on specific types of GUI elements. All the client code works with GUI elements through abstract interfaces (traits) defined by the gui lib.
There are two approaches to implementing abstract factories in Rust:
using generics (static dispatch)
using dynamic allocation (dynamic dispatch)
When you're given a choice between static and dynamic dispatch, there is rarely a clear-cut correct answer. You'll want to use static dispatch in your libraries and dynamic dispatch in your binaries. In a library, you want to allow your users to decide what kind of dispatch is best for them since you don't know what their needs are. If you use dynamic dispatch, they're forced to do the same, whereas if you use static dispatch, they can choose whether to use dynamic dispatch or not.
gui: Abstract Factory and Abstract Products
macos-gui: One family of products
windows-gui: Another family of products
Here, the abstract factory is implemented via generics which lets the compiler create a code that does NOT require dynamic dispatch in runtime.
app: Client code with static dispatch
If a concrete type of abstract factory is not known at the compilation time, then is should be implemented using Box pointers.