Friday, January 26, 2024

null safety? Dart vs Null References: The Billion Dollar Mistake

Understanding null safety | Dart

When Dart first launched, compile-time null safety was a rare feature needing a long introduction. Today, Kotlin, Swift, Rust, and other languages all have their own answers to what has become a very familiar problem...

If you run this Dart program without null safety, it throws a NoSuchMethodError exception on the call to .length. The null value is an instance of the Null class, and Null has no “length” getter. Runtime failures suck. This is especially true in a language like Dart that is designed to run on an end-user’s device. If a server application fails, you can often restart it before anyone notices. But when a Flutter app crashes on a user’s phone, they are not happy. When your users aren’t happy, you aren’t happy.

The Dart language is type safe: it uses a combination of static type checking and runtime checks to ensure that a variable’s value always matches the variable’s static type, sometimes referred to as sound typing. Although types are mandatory, type annotations are optional because of type inference.

Speaking at a software conference in 2009, Tony Hoare hyperbolically apologized for "inventing" the null reference:[26] [27]
"I call it my billion-dollar mistake. It was the invention of the null reference in 1965. At that time, I was designing the first comprehensive type system for references in an object oriented language (ALGOL W). My goal was to ensure that all use of references should be absolutely safe, with checking performed automatically by the compiler. But 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.[28]"

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