Rust 1.33を早めに深掘り

オプティムのテックブログがRustブログと化してきた今日この頃、皆様いかがお過ごしでしょうか。R&Dチームの齋藤です。

本日、日本時間2019/03/01(金)にRust 1.33がリリースされました。この記事ではRust 1.33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、翻訳・追記をしています。

また、公式のブログ記事も参考にしてみてください。

f:id:optim-tech:20190301145156p:plain

言語
コンパイラ
ライブラリ
安定化されたAPI
Cargo
互換性メモ
関連リンク
さいごに
ライセンス表記

言語

`cfg(target_vendor)`が使えるようになった

vendorは基本的にはtripleの先頭から2つ目の部分を指す。

x86_64-apple-darwin: apple
x86_64-pc-windows-gnu: pc
i686-unknown-linux-gnu: unknown
wasm32-unknown-unknown: unknown
armv7-linux-androideabi: unknown
i686-unknown-netbsd: unknown
thumbv6m-none-eabi: (空文字列)

これらはrust-lang/rust/src/librustc_target/spec以下で定義されている。

整数型が網羅的（exhaustive）にパターンマッチするようになった

match式で_ => unreachable!()を入れる必要がなくなった。ということは、特に意味は無いがこんな風にも書ける。

fn main() {
    let x = 100u8;
    let 0..=255 = x;
}

`if let`や`while let`で複数の条件を書けるようになった

今までmatch式を使っていた所がifによって読みやすくなる。

enum Creature {
    Crab(String),
    Lobster(String),
    Person(String),
}

fn main() {
    let state = Creature::Crab("Ferris".to_string());

    if let Creature::Crab(name) | Creature::Person(name) = state {
        println!("This creature's name is: {}", name);
    }
}

`if let`や`while let`での反駁不能パターンがエラーから警告になった

反駁不能（irrefutable、他の意見が通らない状態＝常に真になるパターンのようなもの）がエラーではなく警告として扱われるようになった。汎用的マクロでのマッチングが使えるようになる。

`const`関数でいくつかの機能が使えるようになった

C++14のconstexpr関数に近づいた。下記が使えるようになった機能。

let
let mut
- 代入も可
式
反駁不能な分解パターン

`const unsafe`関数が`const`関数から呼べるようになった

const unsafe fn foo() -> i32 { 5 }
const fn bar() -> i32 {
    unsafe { foo() }
}

`cfg_attr`属性に複数の属性を入れられるようになった

今までは2行に分けていたものが1行で書けるようになる。

#[cfg_attr(all(), must_use)]
#[cfg_attr(all(), allow(unused))]
fn old_cfg_attr() {
}

#[cfg_attr(all(), must_use, allow(unused))]
fn new_cfg_attr() {
}

`#[repr(packed)]`属性によってアライメントを指定出来るようになった

#[repr(packed(2))] struct Foo(i16, i32);は2バイトのアライメントを持ち、サイズは6バイトとなる。これを指定しない場合、64ビット環境では8バイトアライメントとなり、16バイトの構造体となってしまう。

インポートするとき、`_`を使えるようになった

一見無意味のように思えるが、トレイトは名前を持つ意味がないものの名前を与える必要があった。これによって同じ名前のトレイトが使えるようになった。

use std::io::Read as _;

// 単一の`Read`トレイトとして使える
pub trait Read {}

`extern`関数がパニックした時にはデフォルトでabortするようになった

以前は未定義とされていた。

コンパイラ

rustcに引数-Clinker-flavorを追加することでリンカーの種類を指定出来るようになった
LLVMの最低バージョンが6.0に引き上げられた
PowerPC64アーキテクチャ上のFreeBSDがサポートされた
ターゲットx86_64-fortanix-unknown-sgxがTier 2サポートに格上げされた。 Rustがサポートするプラットフォームの情報はplatform supportを参照のこと
thumbv7neon-linux-androideabiとthumbv7neon-unknown-linux-gnueabihfのターゲットがサポートされた
x86_64-unknown-uefiのターゲットがサポートされた

ライブラリ

// &mut u8を引数に取り、&u8を返す関数を受け取る
fn test<F: Fn(&mut u8) -> &u8>(f: F) {
    f(&mut 0);
}

fn main() {
    test(|x| x);
    // identityだとエラー
    // test(std::convert::identity);
}

従って、引数の型と戻り値の型が明確に同じであることを保証出来る。これは、変数を明示的に破棄するmem::dropと似た立ち位置と言える。

Cargo

初期ビルド中にファイルが変更された場合、Cargoはそのクレートを再ビルドするようになった

互換性メモ

標準ライブラリのメソッドstr::{trim_left, trim_right, trim_left_matches, trim_right_matches}が非推奨になった
- RTL言語においては逆の挙動を示すため。代わりにstr::{trim_start, trim_end, trim_start_matches, trim_end_matches}を使うこと。

さいごに

整数型の網羅的マッチやif letでの複数条件はかゆい所に手が届くアップデートで助かります。今後もRustの進化から目が離せませんね。

オプティムでは最新の言語仕様を追うのが好き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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OPTiM TECH BLOG

Rust 1.33を早めに深掘り

言語

`cfg(target_vendor)`が使えるようになった

整数型が網羅的（exhaustive）にパターンマッチするようになった

`if let`や`while let`で複数の条件を書けるようになった

`if let`や`while let`での反駁不能パターンがエラーから警告になった

`const`関数でいくつかの機能が使えるようになった

`const unsafe`関数が`const`関数から呼べるようになった

`cfg_attr`属性に複数の属性を入れられるようになった

`#[repr(packed)]`属性によってアライメントを指定出来るようになった

インポートするとき、`_`を使えるようになった

`extern`関数がパニックした時にはデフォルトでabortするようになった

コンパイラ

ライブラリ

安定化されたAPI

`unix::FileExt::read_exact_at`

`unix::FileExt::write_all_at`

`Option::transpose`

`Result::transpose`

`convert::identity`

`pin::Pin`

`marker::Unpin`

`marker::PhantomPinned`

`Vec::resize_with`

`VecDeque::resize_with`

`Duration::as_millis`

`Duration::as_micros`

`Duration::as_nanos`

Cargo

互換性メモ

関連リンク

さいごに

ライセンス表記