TL;DR: Null is schizofrenic and does not exist in real world. His creator regreted and programmers around the world suffer it. Don't be a part of it.

문제

솔루션

예외

샘플 코드

잘못된

class CartItem{
  constructor(price) {
     this.price = price;
  }
}

class DiscountCoupon {
  constructor(rate){
    this.rate = rate;
  } 
}

class Cart{        
    constructor(selecteditems, discountCoupon){
        this.items = selecteditems;
        this.discountCoupon = discountCoupon;
    }     
    subtotal(){    
        return this.items.reduce((previous, current) => previous + current.price, 0);      
    }  
    total(){    
        if (this.discountCoupon == null)
          return this.subtotal();
        else
          return this.subtotal() * (1 - this.discountCoupon.rate);      
    }
}

cart = new Cart([new CartItem(1), new CartItem(2), new CartItem(7)], new DiscountCoupon(0.15));
//10 - 1.5 = 8.5

cart = new Cart([new CartItem(1), new CartItem(2), new CartItem(7)], null);
//10 - null  = 10

오른쪽

class CartItem{
  constructor(price) {
     this.price = price;
  }
}

class DiscountCoupon {
  constructor(rate){
    this.rate = rate;
  } 
  discount(subtotal){
    return subtotal * (1 - this.rate);    
  }
}

class NullCoupon {    
  discount(subtotal){
    return subtotal;    
  }
}

class Cart{        
    constructor(selecteditems, discountCoupon){
        this.items = selecteditems;
        this.discountCoupon = discountCoupon;
    }     
    subtotal(){    
        return this.items.reduce((previous, current) => previous + current.price, 0);      
    }  
    total(){    
        return this.discountCoupon.discount(this.subtotal());      
    }
}

cart = new Cart([new CartItem(1), new CartItem(2), new CartItem(7)], new DiscountCoupon(0.15));
//10 - 1.5 = 8.5

cart = new Cart([new CartItem(1), new CartItem(2), new CartItem(7)], new NullCoupon());
//10 - nullObject  = 10

발각

태그

결론

더 많은 정보

학점

I couldn't resist the temptation to put in a null reference, simply because it was so easy to implement. This has led to innumerable errors, vulnerabilities, and system crashes, which have probably caused a billion dollars of pain and damage in the last forty years.