Maxi ContieriProgrammers use Null as different flags. It can hint an absence, an undefined value, en error etc.
Multiple semantics lead to coupling and errors.
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.
Problems
Coupling among the callers and the senders.
Mismatch among the callers and the senders.
If/Switch/Case Polluting.
Null is not polymorphic with real objects. Hence, Null Pointer Exception
Null does not exist on real world. Thus, it violates Bijection Principle
Solutions
Avoid Null.
Use NullObject pattern to avoid ifs.
Use Optionals.
Exceptions
- APIs, Databases and external systems where NULL does exist.
Sample Code
Wrong
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
Right
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
Detection
Most Linters can show null usages and warn us.
Tags
- Null
Conclusion
- Null is the billion-dollar mistake. Yet, most program languages support them and libraries suggest its usage.
More info
Credits
Photo by Kurt Cotoaga on Unsplash
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.
Tony Hoare
This article is part of the CodeSmell Series.
Last update: 2021/06/16
