Bump Rust version to 1.56.0

[TonalidadeHidrica]

Currently, the MSRV (Minimum Supported Rust Version) is essentially 1.42.0, which is intednded to work in AtCoder.
Now that AtCoder is updating the version, it may be a good idea to bump supported version, so that we can now use 2021 Edition and various new features.

However we also need to consider other websites (CodeForces, yukicoder, ...) too. I'm going to survey the Rust versions used in other platforms and post them as a succeeding comment.

[TonalidadeHidrica]

Here is a collection of "famous" online judge sites, accompanied by available rust versions. (The choice is very subjective. Feel free to suggest other websites that are somewhat famous. I also tried to include as much Japanese judges as possible.)

• AtCoder: 1.42.0 -> 1.68.1
• CodeForces: 1.66.0 (could not find a blog post)
• TopCoder: not supported
• CodeChef: 1.56
• oj.uz: not supported?
• LeetCode: 1.58.2
• HackerRank: 1.59.0
• Sphere Online Judge (SPOJ): 1.56
• CS Academy: 1.61.0
• yukicoder: 1.68.1 (2021) (Updated on 2023-04-17)
• PKU (Peking University) Online Judge (POJ): not supported
• Library Checker: 1.60.0
• Google Code Jam (GCJ): 1.41.0 (will be closed on 2023-07-01 😢)
• Aizu Online Judge (AOJ): 1.41.1
• Hamako Online Judge (HOJ): not supported
• Kotamanegi Online Judge: not supported
• Kagamiz Contest System (KCS): down
• CafeCoder: down
• MojaCoder: 1.43.0 (could not find an official source)
• paiza: 1.59.0
• CodInGame: 1.60.0

FYI:

• Rust 2018 Edition was stablized since 1.31.0.
• Rust 2021 Edition was stablized since 1.56.0.

See also this Wiki, which is not as comprehensive as this list, but contains some more useful information.

---

Basically, I think we may bump MSRV to Rust 1.56.0, adopting Rust 2021. Apart from GCJ, the only websites that will be no longer supported are AOJ and MojaCoder. Do you think it is OK, or shuold we stick to 1.42-ish versions?

[TonalidadeHidrica]

My bad, I shuold have checked #83 first. Anyway, this issue suggests a completely different direction from #83 , and I want other users' opinions.

[TonalidadeHidrica]

One possible downside of upgrading the edition to 2021 is that it may no longer compile when "expanded."

[mizar]

• yukicoder: 1.59.0 (2018)

yukicoder Bumped 1.68.1 (2021).

[togatoga]

@TonalidadeHidrica

Thank you for bringing this topic. I think it's enough to stick with AtCoder platform because ac-library-rs is a rust port of AtCoder Library.
For me, it's super painful to keep using 1.42.0 version because some platforms seem not to support 1.42.0.
I want to bump the version as soon as possible.

[koba-e964]

Universal Cup (contest.ucup.ac) seems to support Rust 1.66.0.
(evidence: the following code

fn main() {
// 1.66.0
let x = Some((1, "hi"));
let y = None::<(u8, u32)>;

assert_eq!(x.unzip(), (Some(1), Some("hi")));
assert_eq!(y.unzip(), (None, None));
// 1.67.0
assert_eq!(5i32.checked_ilog(5), Some(1));
}

emits a compilation error: https://contest.ucup.ac/submission/225227)

Maybe somewhere between 1.60.0 and 1.70.0 should be fine.

[koba-e964]

Personal opinion: we want to support AtCoder (1.70.0) and Codeforces (1.72.0) because:

• AtCoder is the primary objective of this project
• Codeforces wields the biggest stick in competitive programming

All other platforms are insignificant compared to these two, so we can update to 1.70.0.

[koba-e964]

Closing because #137 was merged.