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What is (double (^)(int))foofoo
I've tried searching for a definition on Google and SO and I found examples in which they are used but not clearly defined. By "block" I mean the caret symbol (^). I found it on a site where cdecl they described:
(double (^)(int, long long )) foo
as
cast foo into block(int, long long) returning double
I've never once seen this symbol used before today. Can anyone clearly describe what a block is and include with it a minimal working example? Thanks.
Blocks are a non-standard extension to the C (and not only to the Objective-C) language by Apple. They realize closures (lambda functions, etc., however you call them) - basically they're unnamed function-like entities, enclosing code that can be called. They facilitate writing for example event-driven code, where callbacks are used exhaustively.
来源：https://stackoverflow.com/questions/12270079/what-is-a-block-in-c