Robert Fischer has a bad day with REXML: "In this language core library, both versions are broke! The solution is for me to reach in and make a change to the core library so that we avoid a null. In the standard Ruby deployment, using the standard core XML processing library, there is no way to write out XML. It is impossible because of bugs in the library.
The worst part?
THAT STUPID BUG IN THEIR CORE LIBRARY WOULD HAVE BEEN FIXED WITH STATIC TYPING. Even more if you have a type system which can check nulls for you."
I think it would be unfair to paint Ruby with REXML's brush. Even if static typing would fix some problems, I can't imagine Rails built on a language with a static type system. As we'll see in a minute you can write a good XML library without static typing. According to DHH "I think Rails feels, smells, and tastes like it does exactly because its very Ruby-like". Now the dilemma:
"I’ve cut Ruby on Rails a lot of slack, because the bugs and the awkwardness are the price that you pay to hang out with the beer-swilling hipsters that make out that community and roll with the rapid rate of development. And, really, it is the best web framework I’ve dealt with, mainly because it provides the most comprehensive and extensible set of functionality of any framework, and it’s got a solid community to back it up."
Fwiw, this is the reason I default to Django - similar to Robert's experience with Rails, I find it provides a comprehensive and extensible set of functionality, and it’s got a solid community to back it up. Plus it's fun. Django is written in Python and Python's libraries tend to be well baked. In particular there are ones outside distro that rock. If there's a better XML lib than Elementtree, I don't know what it is. If there's a better httplib than httplib2, I don't know what it is. PIL. Feedparser. BeautifulSoup. Numeric. And so on. I guess I'm lucky in my choices.
It can take a few attempts to get the design of libraries right - going back to XML for a second, look at how long it took to get to XOM and XStream in Java (neither of which are in the JDK). Embedding libraries with immature designs, usually due to reaction to industry trends, has been a problem for the JDK. Once a lib ships in that core it's very hard to root it out. But when you look at search and megadata problems, no community has anything comparable to mg4j/lucene/hadoop. I remember a time when Python's XML support was up in the air and Unicode was "up the BOM". Python still has problems with installation, whereas Ruby has gems.
That said, library problems are transient problems. They can be fixed.