Hacker News Reader

Comment by ewalk153 | Hacker News Reader

Daniel’s PR to implement this in node.js[1] is case study in:

- crafting a high context yet succinct description

- addressing PR feedback well

- giving respect to a pedantic commenter who understands the inner workings far less than Daniel while not conceded to make a destructive change.

I will share this PR widely as arole model in open source contributions.

[1] https://github.com/nodejs/node/pull/50288

View on HN

The same thing struck me as well. This is one of the best optimization professionals on the planet, showing up with a huge improvement, and receiving some misplaced arrogance.

The lesson here is to always, always watch your own review tone, and not make this mistake.

The other lesson is that when a PR shows up with this kind of technical information attached to it, spend the 60 seconds it takes to Google for "lemire".

I'm surprised that the reviewer was so ignorant of amortized constant time insertion.

I am not at all surprised. Kids these days have no idea what CPUs can do. ;)

I periodically have interview candidates work through problems involving binary search, then switch to bounded and ask them how to make it go faster over N elements, where N is < 1e3. The answer is "just linear search, because CPUs really like to do that".

But amortized analysis has nothing to do with what CPUs can do. CS students learn it in an algorithm course, not in a computer architecture course.

If I'm being super pedantic, I would argue that while `string::push_back` should take amortized constant time, `string::append` has no such guarantee [1]. So it is technically possible for `my_string += "a";` (same to `string::append`) will reallocate every time. Very pedantic indeed, but I have seen some C++ implementation where `std::vector<T>` is an alias to `std::deque<T>`, so...

One thing I don't like about lemire's phrasing is that he only looks at the current, often only most available, implementations and doesn't make this point explicit for most cases.

EDIT: Thankfully he does acknowledge that in a later post [2].

[1] https://timsong-cpp.github.io/cppwp/n4861/strings#string.app...

[2] https://lemire.me/blog/2023/10/23/appending-to-an-stdstring-...

> but I have seen some C++ implementation where `std::vector<T>` is an alias to `std::deque<T>`, so

I have a hard time believing that because std::vector guarantees that the memory is contiguous.

Yeah, it wouldn't be standard-compliant, and I think it was very ancient one---at least as old as STLport I believe.

This feels like a conversation where it would have been useful for the participants to be very explicit about the points they were trying to convey: the reviewer could have said "Isn't this a quadratic algorithm, because each call to `+=` reallocates `escaped_file_path`?" (or whatever their specific concern was; I may have misunderstood), and the author's initial response could have been "No, because the capacity of the string is doubled when necessary."

Reply on news.ycombinator.com