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So, after some thinking, I found the solution: I have to declare a placeholder class inheriting from NSObject, then declare a bunch of function pointers (so it has to be refined a lot!!!). The actual function pointer doing the blocks' job is a function pointer using the return type and arg list plus self of the original block, like this (example code):

    #import <Foundation/Foundation.h>

    void blck(id _self, NSString *line, BOOL *stop) {
        printf("Line: %s\n", [line UTF8String]);
    }

    @interface BlockPlaceholder: NSObject {
        void *block0;
        void *block1;
        void *block2;
        void *block3;
        void *block4;
        void *block5;
        void *block6;
        void *block7;
    }
    @end

    @implementation BlockPlaceholder

    - (id) init {
        self = [super init];
        block0 = block1 = block2 = block3 = block4 = block5 = block6 = block7 = blck;
        return self;
    }

    @end

    int main() {
        NSAutoreleasePool *pool = [NSAutoreleasePool new];
        NSString *lines = @"This\nis\na\ntext\n";
        BlockPlaceholder *block_obj = [[BlockPlaceholder alloc] init];
        [lines enumerateLinesUsingBlock:block_obj];
        [block_obj release];
        [pool release];
        return 0;
    }

And this one does not crash, and outputs:


Line: This
Line: is
Line: a
Line: text

as expected. :-)