If only lawyers could write Perl modules
With so many powerful programming languages freely available, it’s very common for large software systems to use more than one. Write some C, use a scripting language and do some database access and there’s three already. Even if the deployed code is only in one language, test scripts and harnesses often use another. Multiple languages are a good thing if it means the right tool is used for the right job.
But there are annoyances. In particular, violations of the Single Point of Truth (SPOT) rule are common. For example, here’s a C++ enum containing error codes:
enum FooErrors
{
FOOERR_OK = 0,
FOOERR_FILE_NOT_FOUND = 1,
FOOERR_IT_JUST_BORKED = 2,
// further constants follow
};
If the same constants are used by a part of the system written in a different language, the cheap and cheerful solution is just to declare them again:
class FooErrors
{
public static final int FOOERR_OK = 0;
public static final int FOOERR_FILE_NOT_FOUND = 1;
public static final int FOOERR_IT_JUST_BORKED = 2;
// contains all the same constants as in C++
}
This is fine as far as it goes, and I’ll admit that most developers are dealing with bigger problems than a few duplicate declarations. But if the constants are used by more than two languages, keeping everything in sync become a maintenance burden.
I’d like a simple script that acts as a sort of poor-man’s IDL compiler, reading a text file containing names and values and spitting out nicely-formatted declarations in a variety of languages. A new constant would be added by updating the text file, running the script and committing the modified source files to the nearest version control system.
This seems like such an obvious thing to do that I was sure I’d find a Perl module or seven on CPAN to do it. But I couldn’t find anything.
What I did find were two patents describing almost exactly this idea. The first, US Patent 7143400 titled Configuration description language value management method and system, contains this in the summary:
… the present invention fills this need by providing a method and a system for centralizing the maintenance of name value pairs for defining constants and properties used by different portions of a program, where the different portions are of a different programming language type.
The second, US Patent 6964038 titled Constant values in mixed language programming environments, is described as:
a method of and apparatus for maintaining consistency between header files for differing computer program languages. More particularly, the invention relates to automatically generating one or more header files in a programming language based on a header file in a different programming language.
The assignee of the first patent is Sun Microsystems, Inc and the assignee of the second is the Hewlett-Packard Development Company, L.P..
I haven’t read the patents thoroughly, so I guess there could be some patent-worthy ideas in them. Maybe. The thing that irks me is that for what it cost in lawyers to file these two patents you could build the finest constant-generating system the ‘Net has seen, supporting a bunch of languages with all the bells and whistles. And you might just get something useful for your money.
If you know of a good free tool- potentially infringing or not- for this simple problem, please comment.
