ObjC_call_block_with_invocation.m

#import <Foundation/Foundation.h>

static NSMethodSignature *BlockSignature(id blockObj) {

	struct Block {
		void *isa;
		int flags;
		int reserved;
		void *invoke;

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

	struct Block *block = (__bridge void *)blockObj;

	int copyDisposeFlag = 1 << 25;
	int signatureFlag = 1 << 30;

	assert(block->flags & signatureFlag);

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

	const char *types =  block->descriptor->rest[index];
	NSMethodSignature *signature = [NSMethodSignature signatureWithObjCTypes: types];

	while([signature numberOfArguments] < 2) {
		types = [[NSString stringWithFormat: @"%s%s", types, @encode(void *)] UTF8String];
		signature = [NSMethodSignature signatureWithObjCTypes: types];
	}

	return signature;
}

int main(void) {
	@autoreleasepool {
		int captured = 123;

		void (^block)(int, NSString *) = ^(int testArgument, NSString *anotherTestArgument) {
			NSLog(@"%d %d %@", captured, testArgument, anotherTestArgument);
		};

		NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:BlockSignature(block)];
		[invocation setTarget:block];

		[invocation setArgument:&(int){ 456 } atIndex: 1];
		[invocation setArgument:&(NSString *){ @"string" } atIndex: 2];

		[invocation invoke];
	}
}