Good questions, and no. Anecdotally, talking to other Grails developers - ones who have switched from Java - they all acknowledge that they write fewer - often far fewer - lines of code.
I agree on the point that people may just be bad estimators, but I was assuming at least some of them have done approximate LOC counts on their own code from time to time to get estimates. I do.
Agreed. And given that he's just taught the basics of Groovy to the audience, the likelihood of them being able to accurately project how many LOCs it will save them seems pretty low.
That's part of the point, in a way. Not to prove to people how much they don't know in a negative way (but maybe it comes across that way), but to provide a hopefully fairly shocking number to get them to rethink some of their basic assumptions about development. Using even a moderately different toolset can yield dramatically different (and I'd argue usually better) results.
Is there any rigorous study more recent than Lutz Prechelt's "An Empirical Comparison of Programming Languages"? That estimates a factor of two difference in lines of code between Java/C/C++ and Python/Perl/Tcl, albeit for a rather small project.
So I've been using "factor of two" as a rough benchmark. Of course, this assumes appropriate library support; if most of the C code implements a priority queue while C++ has that as part of the standard library, then the comparison is invalid.
I don't know if for this Grails comparison if the extra factor of two comes from Groovy or from the effectiveness of Grails over whatever the Java programmers would use for web app development.
Have you asked Grails/Groovy developers the same question? Have you written equivalent Java code to compare outright?