Add function for generating random values

[laniakea64]

Adds pick() function as discussed in #1991 (comment)

I'm still relatively new to Rust, so code review would be much appreciated 🙂

cc @t3hmrman

[t3hmrman]

If you're into it, you could add some examples of the use to the examples folder -- maybe under the existing kitchen sink ones?

[casey]

I think it's fine not to. I don't really require adding examples for every new function. An example can be added to the readme though.

[t3hmrman]

Hey @laniakea64 thanks for the quick turnaround on this! One more thing that would be awesome are some tests! There's not much you can test (especially as this is real random and not pseudo random), but at the very least the string formation/length might be worth testing!

I wonder if you can easily test entropy (I assume GH runners have enough and this won't be a problem)

[laniakea64]

Hey @laniakea64 thanks for the quick turnaround on this!

You're welcome, thanks for your review!

One more thing that would be awesome are some tests! There's not much you can test (especially as this is real random and not pseudo random), but at the very least the string formation/length might be worth testing!

Done.
(I have no actual idea what I'm doing in this area, I just tried to follow the pattern of how existing functions tests were written and this change passed cargo clippy --all-targets --all-features and cargo test locally.)

I wonder if you can easily test entropy (I assume GH runners have enough and this won't be a problem)

I have no idea how to even start there, sorry 😨

[casey]

Looks good! I think we should this function choose. I was poking around, and that seems to be the most common name.

[casey]

I think it's fine not to. I don't really require adding examples for every new function. An example can be added to the readme though.

[casey]

LGTM!

I just merged #2054, which adds some predefined constants, including HEX which are the lowercase hexidecimal digits. Because HEX is now available, I made choose require alphabet, since it's very short, and maybe a little less confusing to write choose('10', HEX) instead of choose('10') where hex is implied. I made a couple of other small changes to the function, including using map_err to produce the error, and (0..n).map(…).collect() to produce the string, to avoid the for loop.

I actually think that, in the general case, pre-allocating the string length isn't useful. The length of a string is in bytes, but characters may be multiple bytes when encoded in UTF-8.