Reframe null value errors ch06-02-match.md

[gerwitz]

This may be pedantic, but so is Rust!

As written, the prose conflates null value errors with Hoare's "billion dollar mistake". But as quoted earlier, that phrase applies to the creation of null values. What is described here is just one trap that his "mistake" enabled.

I have tried to re-phrase more accurately, but my interest is in correctness rather than my word choices.

[chriskrycho]

Thanks for the suggestion, and I for one appreciate your pedantry (pedants unite! 😂)! However, in this case I think it’s okay as is—I checked exactly how the book frames it, and this is how Chapter 6 initially frames it:

I call it my billion-dollar mistake. At that time, I was designing the first comprehensive type system for references in an object-oriented language. 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.

The problem with null values is that if you try to use a null value as a not-null value, you’ll get an error of some kind. Because this null or not-null property is pervasive, it’s extremely easy to make this kind of error.

It is that latter bit this is referring to. In a void, we could of course rephrase it for maximum precision,¹ but with this as the context, I think the existing phrasing is fine, and we’re trying to keep changes where it’s not strictly an error being corrected to a minimum because of the amount of work involved in print updates.

Again, though, thank you (earnestly!) for the pedantry. 😅

Footnotes

1. Being maximally pedantic: having null references is fine if you must always check them and cannot have unchecked types in your system. ↩

[gerwitz]

My pedantry would be offended, but I certainly understand having a high barrier to changes do to printing! Thanks for the thoughtful reply. 🫡