PRE-PROPOSAL: Source and Encoding keyword (original) (raw)

Howard Lovatt howard.lovatt at iee.org
Sun Mar 15 04:30:33 PDT 2009

Since I proposed a source keyword a while back, http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6519124, I am obviously biased in favour of this proposal. I think the place for source is in the file, since the compiler deals with files. The advantage of a source statement is that it positions Java for the future:

  1. There are many proposals around that would benefit from more syntax changes than is currently possible. The obvious current one is module, instead of burdening every tool with a new parsing technology - just make module a keyword. Remember exotic names are already in coin, therefore you can still call old code that uses module as an identifier.

  2. Many proposals for the language jump through hoops it trying to avoid new keywords (I'm talking about you BGGA). These proposals end up looking nothing like Java as a consequence. Java uses unabbreviated keywords, e.g. extends instead of :, this is part of the character of Java. You need a source statement to enable new keywords and hence enable future extensions that don't appear alien.

  3. When there is a reliable library dating scheme (maybe as part of the modules), then the compiler could enforce this also (this would be true for both -source and source in the file). Reliable library management is something separate, but one in place source will be able to use it.

The argument that the JLS doesn't spell out what the current -source flag does, but would have to if source were added to Java is a bit weak. The -source flag exists, it is documented, that documentation could be moved into JLS. If the documentation is not up to JLS standard then at some point, not necessarily now, it will need improving. Remember that this is nothing new, other than putting it into the file. -source already exists, it already has some documentation (people including compiler writers seem largely happy with its documentation).

My motivation for the source keyword came form network protocols (and similar) that have a version number. This has proved a very successful way of maintaining backward compatibility and still adding new features, the same would be true for a programming language. Since there is not much time for coin there is little that this change would add to 6, other than making module a true keyword, but the big picture is the future changes are much more manageable (it is a future proofing strategy - part of a grand plan).

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