Rust 1.35を早めに深掘り

Minecraftが10周年を迎えたそうですね。そりゃ年も取るはずです。R&Dチームの齋藤（@aznhe21）です。 ずっと1.35でFutureが安定化されると思ってたんですが、どうやら1.36だったようですね。 無駄に悲しい思いをしてしまった・・・。

さて、本日、日本時間5/24(金)、令和最初のアップデートとなるRust 1.35がリリースされました。 この記事ではRust 1.35での変更点を詳しく紹介します。 なお、この記事は公式リリースノートをベースに、意訳・追記をしています。

ピックアップ

個人的に注目する変更点を「ピックアップ」としてまとめました。 全ての変更点を網羅したリストは変更点リストをご覧ください。

Box<FnOnce>が使えるようになった

詳細は下記サイトにありますが、今まではFnOnceをBox化して使うことは出来ませんでした。

これがようやく実現します。

fn main() {
    // ちゃんと使える！
    let f: Box<dyn FnOnce()> = Box::new(|| {});
    f();
}

浮動小数点にcopysignが入った

NumPyを使う人ならRustへの移植がやりやすくなるのでお待ちかねだったのではないでしょうか。 ifで分岐するよりシンプルかつ高速になることが期待出来ます。

fn main() {
    let a = 100.0f64;
    let b = -0.;
    assert_eq!(a.copysign(b), -100.);
}

範囲系の構造体にcontainsが入った

Range/RangeFrom/RangeTo/RangeInclusive/RangeToInclusiveにおいて、 引数の値がその範囲にあるかが分かるメソッドcontainsが入りました。 今まではx >= start && x <= endのように書いていたので、コードが見やすく、バグが生まれにくくなります。

fn main() {
    let v = 100;
    assert!((0..=100).contains(&v));
}

変更点リスト

言語

1. Box<FnOnce>とBox<FnMut>、及びBox<Fn>がそれぞれFnOnce・FnMut・Fnを実装するようになった

2. クロージャを不安全関数として扱えるようになった。

   例：

unsafe fn call_unsafe(func: unsafe fn()) {
   func()
}

pub fn main() {
   unsafe { call_unsafe(|| {}); }
}

コンパイラ

• armv6-unknown-freebsd-gnueabihfとarmv7-unknown-freebsd-gnueabihfをターゲットに追加した
• wasm32-unknown-wasiをターゲットに追加した

ライブラリ

• ThreadをDebugで出力するとき、スレッドIDを表示するようになった
• StdinLockとStdoutLock、及びStderrLockがAsRawFdを実装するようになった
• alloc::SystemがDefaultを実装するようになった
• Debugを詳細出力（{:#?}）するとき、最後のフィールドの末尾にカンマが付くようになった
• char::{ToLowercase, ToUppercase}がExactSizeIteratorを実装するようになった
• すべてのNonZero型がFromStrを実装するようになった
• BufReader::{get_ref, get_mut, into_inner}を呼び出すときにReadトレイト境界が不要になった
• 無引数のdbg!マクロによってファイル名と行番号を表示できるようになった
• str::make_ascii_lowercaseなどでのASCII文字の大文字・小文字化が約4倍速くなった
• hash_map::{OccupiedEntry, VacantEntry}がSyncとSendを実装するようになった

安定化されたAPI

{f32,f64}::copysign

• f32::copysignのドキュメント
• f64::copysignのドキュメント

引数の値と符号を同じにした値を返す。

RefCell::replace_with

• ドキュメント

RefCellの中身を、可変参照引数を伴う関数によって書き換える。

RefMut::map_split

• ドキュメント

RefCellの値への借用を2つに分割する。 主にスライスのsplit_at_mutで使えるようだ。

ptr::hash

• ドキュメント

ポインタのアドレスをハッシュ化する。 ポインタの参照先をハッシュ化するわけではない。

{Range,RangeFrom,RangeTo,RangeInclusive,RangeToInclusive}::contains

• Range::containsのドキュメント
• RangeFrom::containsのドキュメント
• RangeTo::containsのドキュメント
• RangeInclusive::containsのドキュメント
• RangeToInclusive::containsのドキュメント

引数が範囲に収まっているかを返す。

Option::copied

• ドキュメント

Option<&T>のTがCopyトレイトを実装するときに使えるもので、中身の値をコピーしてOption<T>として返す。 実質Option::clonedと同じではあるが、TからCopyトレイトへの実装が消えたときでも誤ってコピーしてしまうことを防止できる。

Cargo

• cdylibをビルドするときにcargo:rustc-cdylib-link-argを設定することリンカへの引数をカスタム出来るようになった 。ただし、これはプラットフォームへの依存性が非常に高い

その他

• muslベースのディストロでネイティブにRustツールチェインが動くようになった

関連リンク

• 公式リリースノート
• 公式ブログ記事
• Rust 1.34の深堀り
• Rust 1.36の深堀り

さいごに

今回はあまり大きな変更も無く、かなり小ぶりなアップデートでした。 とは言えライブラリには小粒でもぴりりと辛いアップデートが入っており、確実に着実に使いやすくなっています。

そう言えば前回書いた噂のstd::future::Futureの安定化ですが、1.36で決定したようです。 早くも1.36が待ちきれない（6週間ぶり2度目）ですね。

オプティムでは未来志向なエンジニアを募集しています。

ライセンス表記

• この記事はApache 2/MITのデュアルライセンスで公開されている公式リリースノートを翻訳・追記をしています
• 冒頭の画像中にはRust公式サイトで配布されているロゴを使用しており、 このロゴはMozillaによってCC-BYの下で配布されています
• 冒頭の画像はいらすとやさんの画像を使っています。いつもありがとうございます

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