Null References: The Billion Dollar Mistake - Tony Hoare

Video is from: https://www.infoq.com/presentations/Null-References-The-Billion-Dollar-Mistake-Tony-Hoare

It deserves to be more widely known and seen.

Summary
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Tony Hoare introduced Null references in ALGOL W back in 1965 "simply because it was so easy to implement", says Mr. Hoare. He talks about that decision considering it "my billion-dollar mistake".


Key Takeaways
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- Null references have historically been a bad idea
- Early compilers provided opt-out switches for run-time checks, at the expense of correctness
- Programming language designers should be responsible for the errors in programs written in that language
- Customer requests and markets may not ask for what's good for them; they may need regulation to build the market
- If the billion dollar mistake was the null pointer, the C gets function is a multi-billion dollar mistake that created the opportunity for malware and viruses to thrive

Introducing null
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- 27:40 This led me to suggest that the null value is a member of every type, and a null check is required on every use of that reference variable, and it may be perhaps a billion dollar mistake.
- 28:00 Modern languages such as C# or Spec# and even Java are introducing the idea of non-null reference parameters, and compile time checking which verifies that they cannot possibly have null values.
- 28:50 The issues of overloading and inheritance make it a lot more difficult to do these when null references were originally created.
- 29:20 The movement must have been made based on the fact that null references were an expensive mistake.