More common way to distinguish values in the RACSignal stream (ReactiveCocoa 2)

RACSignal+DistinctBasedOnRule.m

typedef BOOL(^PassRuleBlock)(id first, id second);

- (RACSignal *)distinctBasedOnRule:(PassRuleBlock)passRuleBlock {
    Class class = self.class;
    
    return [[self bind:^{
        __block id lastValue = nil;
        
        return ^(id x, BOOL *stop) {
            if ((passRuleBlock(x, lastValue) == NO)) { return [class empty]; }
            
            lastValue = x;
            return [class return:x];
        };
    }] setNameWithFormat:@"[%@] -distinctBasedOnRule", self.name];
}