Description Constantine Plotnikov 2022-03-19 14:01:16 EDT

Xtend language implementation itself is closed and does not provide access to the implementation packages. It is reasonable if we consider Xtend a language implementation, so internal packages are closed. But it makes a poor sense if we consider Xtend as an extensible language.

To support heavy-weight extensions (like adding new types of types or new operators) to the Xtend language the following should be done:

1. OSGi packages should be opened for all xtend related modules. This is a minimal first step. This includes Xtend/java code, models and grammar. This need for both: the core language components, compiler, and ide support components.

2. In future, when Xtend grammar is updated, it should be considered how people will extend the grammar. For example, now, if one wants to add a new classifier type, definition of other classifiers needs to be copied.

3. The components like compilers should be open to extension and customization. Final or sealed classes should be avoided for components as first step, and possibly some extension points should be considered to these components to support customizations. The private and package visibility also should be considered more carefully.

4. A sample should be created how to create a heavy-weight extension. A good sample might be entity sample, but refactored as heavy-weight extension (new classifier type) to Xtend. This example might directly reuse "def" from Xtend instead of the custom "op" construct.

These changes will greatly increase value of Xtend in the following areas:

1. A better language research platform for the scientific community 

2. A better teaching material in education context (tasks like adding operator or classifier to the language will become possible as short-term student tasks)

3. A better platform for code generators in commercial and open source projects. Sometimes there is a need for all of Xtend + little extension. Like new classifier type or C#-like Linq queries for JPA using criteria API.