MongoDB relies on key order but doesn’t guarantee it will preserve document key order. Steer clear.

MongoDB document keys are ordered. Subdocument queries fail to retrieve results whose keys are in a different order. Indexing only works with keys in the same order.

I stumbled from the red-eye into the airport shortly after dawn. Bleary-eyed and back on the ground in Atlanta at last, Clojure/West, and its talk of Lisp and browser and JVMs, seemed already a distant memory. My laptop hadn’t left its TSA-friendly bag for the past week. My notebook was full of scribbles and mindmaps. What was a Cocoa programmer to make of it all?

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Sometimes, you want a block to be able to call itself. That means it needs a reference to itself. And that means you have a wonderful opportunity to create a strong reference cycle that will endure till the end of time, or at least till your app exits.

The Solution

__weak __block block_t recurse;
block_t block;
recurse = block = ^(id val) {
    …
    recurse(subval);
    …
}

Getting There

Internationalization is hard. If you’ve always lived where you have to travel to another continent to encounter something other than your local monoculture (hello, many fellow Americans), it’s even harder.

Perhaps it should be no surprise then that everyone gets it wrong. Over and over, I see the same amateur mistakes. Two seconds using your app in some locale other than the one you developed in would make you go, “Oh. Crap.”

Starting with OS X 10.6, you can use the __attribute__ keyword to specify that a Core Foundation property should be treated like an Objective-C object for memory management:

@property(retain) __attribute__((NSObject)) CTFrameRef frame;

This is an easy attribute to miss. It’s also one you can go a long time without finding, because it’s not hard to work around.

(Do note that you can use the NSObject attribute with anything where you’d use CFRetain/CFRelease, not just actual toll-free bridged objects. The toll you’re dodging with __attribute__((NSObject)) is purely syntactic.)