ObjC wrapper block

ObjC_wrapper_block.m

#import <Foundation/Foundation.h>
#import <objc/message.h>

struct BlockDescriptor {
    unsigned long reserved;
    unsigned long size;
    void *rest[1];
};

struct Block {
    void *isa;
    int flags;
    int reserved;
    void *invoke;
    struct BlockDescriptor *descriptor;
};

enum {
    BLOCK_HAS_COPY_DISPOSE =  (1 << 25),
    BLOCK_HAS_CTOR =          (1 << 26), // helpers have C++ code
    BLOCK_IS_GLOBAL =         (1 << 28),
    BLOCK_HAS_STRET =         (1 << 29), // IFF BLOCK_HAS_SIGNATURE
    BLOCK_HAS_SIGNATURE =     (1 << 30),
};

static char *BlockSig(id blockObj) {
    struct Block *block = (__bridge void *)blockObj;
    struct BlockDescriptor *descriptor = block->descriptor;

    assert(block->flags & BLOCK_HAS_SIGNATURE);

    int index = 0;
    if(block->flags & BLOCK_HAS_COPY_DISPOSE)
        index += 2;

    return descriptor->rest[index];
}

@interface MAFakeBlock : NSObject {
    int _reserved;
    IMP _invoke;
    struct BlockDescriptor *_descriptor;
    const char *_types;
    NSMethodSignature *_signature;
}

- (id)initWithTypes:(const char *)types;

@end

@implementation MAFakeBlock

- (id)initWithTypes: (const char *)types {
    if((self = [super init])) {
        _types = types;
        _signature = [NSMethodSignature signatureWithObjCTypes: _types];

        _descriptor = malloc(sizeof(struct BlockDescriptor));
        _descriptor->size = class_getInstanceSize([self class]);
        _descriptor->rest[0] = (void *) _types;

        _invoke = [self methodForSelector: NSSelectorFromString(@"")];
    }
    return self;
}

- (void)dealloc {
    free(_descriptor);
}

- (NSMethodSignature *)methodSignatureForSelector: (SEL)sel {
    return _signature;
}

- (void)forwardInvocation: (NSInvocation *)inv {
    NSUInteger argsCount = [_signature numberOfArguments];
    for (NSUInteger i=0; i<argsCount; ++i) {
        printf("%s", [_signature getArgumentTypeAtIndex:i]);
    }
    printf("\n");
}

- (id)copyWithZone: (NSZone *)zone {
    return self;
}

@end

int main(int argc, char **argv) {
    @autoreleasepool {
        id block = ^(NSString *line, BOOL *stop) {
            NSLog(@"%@", line);
        };

        id intblock = [[MAFakeBlock alloc] initWithTypes:BlockSig(block)];

        NSString *string = @"line1\nline2\nline3";

        [string enumerateLinesUsingBlock:intblock];
    };
}