[doctor_eval]

I much prefer static typing - but the metric used in the article is around bug reduction. Regardless of static (Go or Java), dynamic (JS), or a bit weird (plpgsql), I don’t generally get the type of a variable or object wrong - because when I’m using the object I necessarily must already have a mental map of what it represents. It’s pretty rare to try to call the “fill()” method on a “line” object, so to speak, because I know it’s a line when I access it.

So I’d guess that the number of type related bugs in dynamic languages is just a little bit greater than in static languages, simply because it is harder to make that kind of mistake in a typed language. But as a category, they aren’t common mistakes in the first place.

I can confidently say that I’m a bit of an expert at writing bugs :) and of all the kinds of bugs I write, type related bugs are probably no where near the top of the list.

That’s not to say that static typing isn’t better - I definitely think it is. But I can also believe that it doesn’t necessarily reduce the bug count by a huge margin. (For whatever it’s worth I think the main benefits are documentation and refactoring...)

[the_af]

On that note, I've heard many times dynamic typing advocates say (or write) "I've seldom wrote a bug that was a type error".

But a lot of the time, their language is simply unable to encode certain properties as types, so by definition they don't think of some classes of bugs they do write as "type errors". Maybe in a statically typed languages they would have been type errors indeed!

It's as if the tool you use sometimes reinforces your blind spots: "you don't know what you don't know".

PS: anecdote is probably irrelevant, but I've written plenty of dumb type errors with Python. Things that would have been caught by a test or an external tool, sure, or the type checker of a statically typed language could have caught for me for free, leaving the more relevant logic tests to me. I tend to write type errors left and right. Maybe I'm simply not a good Python programmer, of course!