#import <Foundation/Foundation.h>

@class CalculatorMaker;

typedef CalculatorMaker *(^ReturnBlock)(int);

// Class - CalculatorMaker

@interface CalculatorMaker : NSObject

@property (nonatomic, assign) int result;

- (ReturnBlock)add;

@end

@implementation CalculatorMaker

- (ReturnBlock)add{

    //add被执行，返回一个用于计算的block

    return ^CalculatorMaker *(int x){ //这里的CalculatorMaker *是为了说明问题。日常使用建议用id

        self.result += x;

        return self; //返回了一个CalculatorMaker *

    };

}

@end

// Category - Caculator

@interface NSObject (Caculator)

+ (int)makeCaculators:(void(^)(CalculatorMaker *make))caculatorBlock;

@end

@implementation NSObject (Calculate)

+ (int)makeCaculators:(void(^)(CalculatorMaker *make))caculatorBlock{

    CalculatorMaker *maker = [[CalculatorMaker alloc]init];

    caculatorBlock(maker);

    return maker.result;

}

@end

// main

int main(int argc, const char * argv[]) {

    @autoreleasepool {

        int result = [NSObject makeCaculators:^(CalculatorMaker *maker){

            CalculatorMaker *mk = [[CalculatorMaker alloc]init];

            ReturnBlock blc = mk.add;   //blc为add方法执行后返回的block

            mk = blc();                //执行block后，block返回了一个CalculatorMaker实例

            maker.result = mk.add().add().result;

            //因此，可以直接进行链式编程

            //mk.add返回了一个block,block(2)返回了一个实例(加入叫obj)，这个实例obj执行add,又返回了一个block

            //block又执行block(3)后又返回了一个实例

        }];

        NSLog(@"\nresult = %d",result);

    }

    return ;

}