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Mark Nelson

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Snow Leopard Changes to C

September 09, 2009

Reading through the massive review of Snow Leopard in Ars Technica, I bumped into a little surprise: Apple is extending C to include closures and anonymous functions. 

Honestly, I've never seen a more hardcore review of a minor O/S release than the one that John Siracusa posted last week. His 23 page write-up has the kind of details that would normally take weeks to ferret out. Of particular interest to me was the section on page 9 describing changes in Apple's development environment.

 In the new release of Xcode, Apple has slipped in plugin replacements for the gcc front end, optimizer, and code generator, with conspiracy theorists no doubt seeing a future in which all our compilers belong to Apple.

Of note, Apple has implemented something called blocks, which can be used to create both closures and anonymous functions. Both of these are something that C and C++ programmers could really use - the Standard Template Library would be massively improved by these new types of objects.

What's both interesting and puzzling to me is that John says:

For now, blocks are supported by all four of Apple's compilers in Mac OS X.

This implies of course that the version of gcc shipping with Xcode supports blocks.  Without a hands-on test, I still don't know if this means Apple has forked gcc or the feature was slipped in under the radar. Either possibility seems unlikely.

 Even more amusing is:

It's Apple intention to submit blocks as an official extension to one or more of the C-based languages, though it's not yet clear which standards bodies are receptive to the proposal.

Good luck with that Apple! The C++ committee has been working on the addition of closures for ten years or so, and the end is still not in sight.

The big question this raises in my mind is whether Apple has decided to take ownership of their tool chain. Microsoft has done pretty well with this strategy, but until now, Apple has never done more than wade ankle-deep into things. This Snow Leopard release may signal a change in their thinking.

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