Why can't you reverse a string with a flag emoji?

Maybe I'm missing some prerequisite knowledge here, but why would I assume `flag="us"` is an emoji? Looking at that first block of code, there is no reason for me to think "us" is a single character.

Edit: Turns out my browser wasn't rendering the flags.

Re: Why can't you reverse a string with a flag emoji?

#5

Post by happytoexplain » Thu, Jan 27, 2022, 7:36 PM UTC

I guessed that it would become the USSR flag (US -> SU), but apparently Unicode doesn't define that one! I wonder why. That would have been humorous.

Re: Why can't you reverse a string with a flag emoji?

#6

Post by jerf » Thu, Jan 27, 2022, 7:39 PM UTC

So, in terms of acing interviews, increasingly one of the best answers to the question "Write some code that reverses a string" is that in a world of unicode, "reversing a string" is no longer possible or meaningful.

You'll probably be told "oh, assume US ASCII" or something, but in the meantime, if you can back that up when they dig into it, you'll look really smart.

Re: Why can't you reverse a string with a flag emoji?

#7

Post by michaelsbradley » Thu, Jan 27, 2022, 7:43 PM UTC

See chapter 7 in Hacking the Planet (with Notcurses) for a short treatment of encodings, extended grapheme clusters, etc.

https://nick-black.com/htp-notcurses.pdf#page53

Re: Why can't you reverse a string with a flag emoji?

#8

Post by greenyoda » Thu, Jan 27, 2022, 7:43 PM UTC

yoyohello13 wrote: post #4

Maybe I'm missing some prerequisite knowledge here, but why would I assume `flag="us"` is an emoji? Looking at that first block of code, there is no reason for me to think "us" is a single character. Edit: Turns out my browser wasn't rendering the flags.

In my browser (Firefox on Windows), the thing between the quotes in the first block of code looks like a picture of the US flag cropped to a circle, not like the characters "us".

Re: Why can't you reverse a string with a flag emoji?

#9

Post by codingkev » Thu, Jan 27, 2022, 7:43 PM UTC

Yes, this allows for easy building of flag emojis as long as you know the ISO 3166 two-letter country code.

Example: https://github.com/kennell/flagz/blob/master/flagz.py

Re: Why can't you reverse a string with a flag emoji?

#10

Post by happytoexplain » Thu, Jan 27, 2022, 7:46 PM UTC

jerf wrote: post #6

So, in terms of acing interviews, increasingly one of the best answers to the question "Write some code that reverses a string" is that in a world of unicode, "reversing a string" is no longer possible or meaningful. You'll probably be told "oh, assume US ASCII" or something, but in the meantime, if you can back that up when they dig into it, you'll look really smart.

I would argue that it is possible and meaningful. AFAIK extended grapheme clusters are well defined by the standard, and are very well suited to the default meaning of when somebody says "character", so, given no other information, it's reasonable to reverse a string based on them. I guess the issue is "reverse a string" lacks details, but I think that's different from "not meaningful".