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From: David Chisnall
Subject: Blocks
Date: Sun, 27 Dec 2009 15:37:21 +0000

Hi Everyone,

I've just added a couple of macros to GNUstep that let us use blocks (but not create) without requiring the compiler to support them. This means that we can implement any of the 10.6 methods that take blocks as arguments, without breaking GCC compatibility.

Blocks are basically structures with one field pointing to a function with a hidden first argument (sound familiar?) that is used to pass the block in. If you use the DECLARE_BLOCK_TYPE macro then it will define a block type if one is supported by your compiler. If not, then it will define a structure with the same layout as a block. The CALL_BLOCK macro either calls the function in the structure, or lets the compiler call the block.

To show how to use these, I've implemented NSArray's - enumerateObjectsUsingBlock: method from 10.6.

Let me know if you've got any questions,


P.S. Creating blocks requires clang and a blocks runtime, such as the one in libobjc2.

-- Sent from my Difference Engine

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