Thought Palace

I’d just begun to muse about signing Atom/RSS articles, when Johannes Ernst began blogging about the topic. I had assumed there must be some easy standard way to do it; but the answer turns out to be that there is a standard, but (according to Johannes) it’s far from easy, so much so that it’s nearly unuseable.
 (The problem in a nutshell: Digital signatures operate on raw data, so to sign something you have to be able to convert it to a sequence of bytes to stream through the signature algorithm. Crucially, to verify the signature you have to be able to convert the something you received into the exact same sequence of bytes. That’s no problem for JPEGs or HTTP bodies. But XML describes an abstract tree of nodes and attributes, with many possible text representations for the same data. If you parse some XML and then turn those data structures back into XML, the text will probably not be exactly the same. Specifying a canonical way to textualize an XML document turns out to be really hard since it has to take into account namespaces, entities, whitespace, character encodings and more. Yeesh!)
 The more I think about this the more [...]

Like most geeks, as a kid I not only despised the Cool Kids, but also wanted to be one of them too. My own school-age development trajectory took me from a state of total ignorance of what that required[1], to brave attempts to fit in[2], to a realization that different was cool[3].

Anyway: these days being a Cool Kid is within every geek’s reach. Perhaps that’s because the shared culture has exploded into an uncountable number of fragments, each of which is a tribe with its own parallel hierarchies of coolness. Amen to that.

Just when it seemed, a decade ago, that the programming world had settled on C++ as the lingua franca, the One Language To Rule Them All, instead we got an explosion of new high-level languages that have risen to popularity. Why did this happen? Chiefly because the World-Wide Web has conditioned users to expect five-second delays before any responses to their actions, which provides an environment ideally suited for interpreted, garbage-collected scripting languages. This movement has been encouraged by server vendors like Sun and IBM who are eager to show Web developers the productivity increases they can get by using such languages, especially after they then install massively powerful servers.

Lua is an interesting scripting language. I can’t say I have much familiarity with it; I’ve only read the book, and a couple of papers, and downloaded and built the interpreter (which takes less than a minute). But what I’ve seen of it gives me a warm feeling, like reading a concise little poem, a haiku. It’s a small language, but what’s there is well-considered, and it appears that you can build bigger things (like object models, whether class- or prototype-based) out of its building blocks pretty easily.

The implementation of the Lua 5.0 runtime is also interesting, as described in an excellent paper. One of the smaller details that’s been fascinating me is that Lua, it turns out, uses unique string objects.

When you use any kind of garbage-collected (or ref-counted) framework, string objects accumulate like dust bunnies. I’ve profiled Java apps and seen tens of thousands of instances of java.lang.String. Cocoa apps also have large numbers of NSStrings lying around. Some of these are temporary strings that just haven’t been garbage-collected (or drained from an autorelease pool) yet; but I think a lot more of them are duplicates.

Lua’s approach, which I have to say I hadn’t thought of before, is [...]