{"id":45519,"date":"2023-10-25T11:37:43","date_gmt":"2023-04-14T00:12:13","guid":{"rendered":"https:\/\/www.silicloud.com\/zh\/blog\/45519-2\/"},"modified":"2024-05-04T05:53:36","modified_gmt":"2024-05-03T21:53:36","slug":"45519-2","status":"publish","type":"post","link":"https:\/\/www.silicloud.com\/zh\/blog\/45519-2\/","title":{"rendered":""},"content":{"rendered":"

\u3053\u306e\u8a18\u4e8b\u306f Rust\u305d\u306e2 Advent Calendar 2018 \u306e15\u65e5\u76ee\u306e\u8a18\u4e8b\u3067\u3059\u3002<\/p>\n

\u8a18\u4e8b\u3092\u66f8\u304f\u3068\u304d\u306b\u4f7f\u7528\u3057\u3066\u3044\u308bRust\u306e\u30d0\u30fc\u30b8\u30e7\u30f3\u306f1.31.0\u3067\u3059\u3002<\/p>\n

const fn\u3068\u306f<\/h1>\n

Rust 2018\u304b\u3089\u4f7f\u3048\u308b\u3088\u3046\u306b\u306a\u3063\u305f\u5b9a\u6570\u3092\u8fd4\u3059\u95a2\u6570\u3002
\n\u5b9f\u884c\u6642\u306b\u547c\u3073\u51fa\u3059\u3053\u3068\u3082\u3067\u304d\u308b\u306a\u3069C++\u306econstexpr\u306b\u4f3c\u3066\u3044\u308b\u3002<\/p>\n

\n

\u30b3\u30f3\u30d1\u30a4\u30eb\u6642\u547c\u3073\u51fa\u3057<\/p>\n

const<\/span> fn<\/span> const_fn<\/span>()<\/span> -><\/span> i32<\/span> {<\/span>\r\n    0<\/span>\r\n}<\/span>\r\n\r\nfn<\/span> main<\/span>()<\/span> {<\/span>\r\n    const<\/span> V<\/span>:<\/span> i32<\/span> =<\/span> const_fn<\/span>();<\/span> \/\/ \u5b9a\u6570\u3092\u8fd4\u3059<\/span>\r\n    assert_eq!<\/span>(<\/span>V<\/span>,<\/span> 0<\/span>);<\/span>\r\n}<\/span>\r\n<\/code><\/pre>\n
\u5b9f\u884c\u6642\u547c\u3073\u51fa\u3057<\/p>\n
const<\/span> fn<\/span> const_fn<\/span>()<\/span> -><\/span> i32<\/span> {<\/span>\r\n    0<\/span>\r\n}<\/span>\r\n\r\nfn<\/span> main<\/span>()<\/span> {<\/span>\r\n    let<\/span> v<\/span>:<\/span> i32<\/span> =<\/span> const_fn<\/span>();<\/span>\r\n    assert_eq!<\/span>(<\/span>v<\/span>,<\/span> 0<\/span>);<\/span>\r\n}<\/span>\r\n<\/code><\/pre>\n
\u5f15\u6570<\/h2>\n
\u5f15\u6570\u3092\u53d7\u3051\u53d6\u308b\u4e8b\u3082\u3067\u304d\u308b\u3002<\/p>\n
const<\/span> fn<\/span> const_fn<\/span>(<\/span>a<\/span>:<\/span> i32<\/span>,<\/span> b<\/span>:<\/span> i32<\/span>)<\/span> -><\/span> i32<\/span> {<\/span>\r\n    a<\/span> +<\/span> b<\/span>\r\n}<\/span>\r\n\r\nfn<\/span> main<\/span>()<\/span> {<\/span>\r\n    const<\/span> V<\/span>:<\/span> i32<\/span> =<\/span> const_fn<\/span>(<\/span>1<\/span>,<\/span> 2<\/span>);<\/span>\r\n    assert_eq!<\/span>(<\/span>V<\/span>,<\/span> 3<\/span>);<\/span>\r\n}<\/span>\r\n<\/code><\/pre>\n
\u5f15\u6570\u306f\u53c2\u7167\u3067\u53d7\u3051\u53d6\u308b\u3053\u3068\u3082\u3067\u304d\u308b\u304cmut\u3067\u53d7\u3051\u53d6\u308b\u3053\u3068\u306f\u3067\u304d\u306a\u3044\u3002
\n\u30e9\u30a4\u30d5\u30bf\u30a4\u30e0\u3092\u6307\u5b9a\u3059\u308b\u3053\u3068\u306f\u3067\u304d\u308b\u3002<\/p>\n
\u5236\u9650<\/h2>\n
\u8ffd\u8a18: 2020\/08\/29
\n1.46.0\u6642\u70b9\u3067\u304b\u306a\u308a\u306e\u5236\u9650\u304c\u306a\u304f\u306a\u3063\u305f\u305f\u3081\u3053\u306e\u9805\u76ee\u306e\u5185\u5bb9\u306f\u300c\u904e\u53bb\u306e\u30d0\u30fc\u30b8\u30e7\u30f3\u306f\u5236\u9650\u304c\u591a\u304f\u3066\u5927\u5909\u3060\u3063\u305f\u3093\u3060\u306a\u300d\u304f\u3089\u3044\u306e\u6c17\u6301\u3061\u3067\u8aad\u3093\u3067\u304f\u3060\u3055\u3044\u3002<\/p>\n
\n
\u95a2\u6570\u5185\u3067if\u306a\u3069\u3092\u4f7f\u304a\u3046\u3068\u3059\u308b\u3068\u4e0b\u8a18\u306e\u3088\u3046\u306a\u30a8\u30e9\u30fc\u304c\u51fa\u308b\u3002
\nerror: `if`, `match`, `&&` and `||` are not stable in const fn<\/p>\n
\u3064\u307e\u308aif\u3082match\u3082&&\u3082||\u3082\u4f7f\u3048\u306a\u3044\u306e\u3067\u3002<\/p>\n
const<\/span> fn<\/span> is_even<\/span>(<\/span>v<\/span>:<\/span> i32<\/span>)<\/span> -><\/span> bool<\/span> {<\/span>\r\n    v<\/span> !=<\/span> 0<\/span> &&<\/span> v<\/span> %<\/span> 2<\/span> ==<\/span> 0<\/span>\r\n}<\/span>\r\n<\/code><\/pre>\n
\u3053\u3093\u306a\u95a2\u6570\u3082\u30b3\u30f3\u30d1\u30a4\u30eb\u30a8\u30e9\u30fc\u306b\u306a\u308b\u3002
\n\u305f\u3060\u3057&\u306f\u4f7f\u3048\u308b\u306e\u3067\u4e0b\u8a18\u306f\u554f\u984c\u306a\u3044\u3002<\/p>\n
const<\/span> fn<\/span> is_even<\/span>(<\/span>v<\/span>:<\/span> i32<\/span>)<\/span> -><\/span> bool<\/span> {<\/span>\r\n    (<\/span>v<\/span> !=<\/span> 0<\/span>)<\/span> &<\/span> (<\/span>v<\/span> %<\/span> 2<\/span> ==<\/span> 0<\/span>)<\/span>\r\n}<\/span>\r\n<\/code><\/pre>\n
\u30a8\u30e9\u30fc\u30e1\u30c3\u30bb\u30fc\u30b8\u306b\u306f\u8868\u793a\u3055\u308c\u3066\u3044\u306a\u304b\u3063\u305f\u304cloop\u3082while\u3082\u4f7f\u3048\u306a\u3044\u3002
\n\u95a2\u6570\u5185\u3067\u5b9a\u6570\u306f\u5b9a\u7fa9\u3067\u304d\u308b\u304c\u5909\u6570\u306f\u5b9a\u7fa9\u3067\u304d\u306a\u3044\u3002<\/p>\n
const<\/span> fn<\/span> const_fn<\/span>()<\/span> {<\/span>\r\n    const<\/span> V<\/span>:<\/span> i32<\/span> =<\/span> 0<\/span>;<\/span> \/\/ OK<\/span>\r\n    let<\/span> v<\/span>:<\/span> i32<\/span> =<\/span> 0<\/span>;<\/span>   \/\/ Error<\/span>\r\n}<\/span>\r\n<\/code><\/pre>\n
\u5909\u6570\u304c\u4f7f\u3048\u306a\u3044\u306e\u3067for\u3082\u4f7f\u3048\u306a\u3044\u3002
\n\u95a2\u6570\u306e\u5f15\u6570\u3092&mut\u3059\u308b\u3053\u3068\u3082\u3067\u304d\u306a\u3044\u3002<\/p>\n
\u4f7f\u3048\u306a\u3044\u3082\u306e<\/h3>\n
    \n
  • \n
      if<\/ul>\n<\/li>\n<\/ul>\n
       <\/p>\n
        \n
      • \n
          match<\/ul>\n<\/li>\n<\/ul>\n
           <\/p>\n
            \n
          • \n
              loop<\/ul>\n<\/li>\n<\/ul>\n
               <\/p>\n
                \n
              • \n
                  \u5909\u6570<\/ul>\n<\/li>\n<\/ul>\n
                  for(\u5909\u6570\u304c\u4f7f\u3048\u306a\u3044\u306e\u3067)
                  \n&&
                  \n||
                  \n\u95a2\u6570\u306e\u5f15\u6570\u3092&mut\u306b\u3059\u308b
                  \n\u95a2\u6570\u5185\u90e8\u3067const fn\u3067\u306f\u306a\u3044\u95a2\u6570\u3092\u547c\u3073\u51fa\u3059
                  \n\u95a2\u6570\u30dd\u30a4\u30f3\u30bf<\/p>\n
                  \u611f\u60f3<\/h1>\n
                  \u4f7f\u3044\u6240\u304c\u304b\u306a\u308a\u9650\u3089\u308c\u308b\u3002
                  \n\u3068\u3044\u3046\u304b\u81ea\u5206\u306f\u4f7f\u3046\u3053\u3068\u304c\u306a\u3055\u305d\u3046\u3002
                  \n\u4f7f\u3044\u6240\u304c\u3042\u308c\u3070\u8ab0\u304b\u6559\u3048\u3066\u304f\u3060\u3055\u3044\u3002<\/p>\n
                  C++11\u306econstexpr\u306f\u6761\u4ef6\u6f14\u7b97\u5b50\u3068\u304b\u30aa\u30fc\u30d0\u30fc\u30ed\u30fc\u30c9\u3068\u304b\u3067\u591a\u5c11\u8907\u96d1\u306a\u51e6\u7406\u304c\u3067\u304d\u305f\u304cRust\u3060\u3068\u305d\u308c\u3082\u3067\u304d\u306a\u3044\u3002<\/p>\n
                  \n
                  \u308f\u304b\u3063\u305f\u3053\u3068\u304c\u5897\u3048\u305f\u3089\u8ffd\u52a0\u3059\u308b\u3068\u601d\u3044\u307e\u3059\u3002<\/p>\n
                  \u8ffd\u52a0<\/h1>\n
                  abs\u306e\u5b9f\u88c5\u306f\u3067\u304d\u305f\u3002<\/h2>\n
                  Rust\u306econst fn\u3067abs<\/p>\n
                  1.33.0\u3067\u4e00\u90e8\u306e\u5236\u9650\u304c\u7de9\u548c\u3055\u308c\u305f<\/h2>\n
                  Rust\u306econst fn\u306e\u5236\u9650\u304c\u7de9\u548c\u3055\u308c\u305f(Rust 1.33.0)<\/p>\n
                  1.46.0\u3067\u3055\u3089\u306b\u5236\u9650\u304c\u7de9\u548c\u3055\u308c\u305f<\/h2>\n
                  Rust\u306econst fn\u306e\u5236\u9650\u304c\u3055\u3089\u306b\u7de9\u548c\u3055\u308c\u305f(Rust 1.46.0)<\/p>\n","protected":false},"excerpt":{"rendered":"
                  \u3053\u306e\u8a18\u4e8b\u306f Rust\u305d\u306e2 Advent Calendar 2018 \u306e15\u65e5\u76ee\u306e\u8a18\u4e8b\u3067\u3059\u3002 \u8a18\u4e8b\u3092\u66f8\u304f\u3068\u304d\u306b […]<\/p>\n","protected":false},"author":4,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-45519","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"yoast_head":"\n- Blog - Silicon Cloud<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.silicloud.com\/zh\/blog\/45519-2\/\" \/>\n<meta property=\"og:locale\" content=\"zh_CN\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:description\" content=\"\u3053\u306e\u8a18\u4e8b\u306f Rust\u305d\u306e2 Advent Calendar 2018 \u306e15\u65e5\u76ee\u306e\u8a18\u4e8b\u3067\u3059\u3002 \u8a18\u4e8b\u3092\u66f8\u304f\u3068\u304d\u306b […]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.silicloud.com\/zh\/blog\/45519-2\/\" \/>\n<meta property=\"og:site_name\" content=\"Blog - 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