{"id":116915,"date":"2026-10-22T09:00:41","date_gmt":"2026-10-22T01:00:41","guid":{"rendered":"https:\/\/www.wsisp.com\/helps\/116915.html"},"modified":"2026-10-22T09:00:41","modified_gmt":"2026-10-22T01:00:41","slug":"c-%e9%80%86%e5%8f%98%e4%b8%8e%e5%8d%8f%e5%8f%98%e5%85%a8%e8%a7%a3%e6%9e%90%ef%bc%9a%e7%9c%8b%e6%87%82%e6%b3%9b%e5%9e%8b%e9%87%8c%e7%9a%84-in-%e5%92%8c-out%ef%bc%8c%e6%8e%a5%e5%8f%a3%e4%b8%8e","status":"publish","type":"post","link":"https:\/\/www.wsisp.com\/helps\/116915.html","title":{"rendered":"C# \u9006\u53d8\u4e0e\u534f\u53d8\u5168\u89e3\u6790\uff1a\u770b\u61c2\u6cdb\u578b\u91cc\u7684 `in` \u548c `out`\uff0c\u63a5\u53e3\u4e0e\u59d4\u6258\u4e0d\u518d\u7ed5\uff01"},"content":{"rendered":"

\u4e00\u53e5\u8bdd\u6982\u62ec： \u534f\u53d8（out）\u8ba9\u201c\u66f4\u5177\u4f53\u7684\u7ed3\u679c\u201d\u53ef\u4ee5\u5f53\u6210\u201c\u66f4\u901a\u7528\u7684\u7ed3\u679c\u201d\u6765\u7528；\u9006\u53d8（in）\u8ba9\u201c\u80fd\u5904\u7406\u66f4\u901a\u7528\u6570\u636e\u7684\u65b9\u6cd5\u201d\u4e5f\u80fd\u5904\u7406\u66f4\u5177\u4f53\u7684\u6570\u636e\u3002\u7406\u89e3\u5b83\u4eec，\u5c31\u80fd\u770b\u61c2 IEnumerable<T>\u3001Action<T>\u3001Func<T, TResult> \u80cc\u540e\u7684\u7c7b\u578b\u8f6c\u6362\u89c4\u5219\u3002<\/p>\n

\u6587\u7ae0\u76ee\u5f55<\/h3>\n
  • \u4e3a\u4ec0\u4e48\u5b66\u4e86\u7ee7\u627f，\u8fd8\u4f1a\u88ab\u6cdb\u578b\u7c7b\u578b\u8f6c\u6362\u96be\u4f4f<\/li>\n
  • \u5148\u641e\u61c2\u4e00\u4e2a\u524d\u63d0：\u6d3e\u751f\u7c7b\u53ef\u4ee5\u5f53\u57fa\u7c7b\u7528<\/li>\n
  • \u4e3a\u4ec0\u4e48 List<Dog> \u4e0d\u80fd\u76f4\u63a5\u5f53\u6210 List<Animal><\/li>\n
  • \u534f\u53d8：out \u8ba9\u201c\u8fd4\u56de\u66f4\u5177\u4f53\u7684\u7c7b\u578b\u201d\u53d8\u5f97\u7075\u6d3b<\/li>\n
  • \u9006\u53d8：in \u8ba9\u201c\u63a5\u6536\u66f4\u901a\u7528\u7684\u7c7b\u578b\u201d\u4e5f\u80fd\u5904\u7406\u5177\u4f53\u5bf9\u8c61<\/li>\n
  • \u81ea\u5b9a\u4e49\u6cdb\u578b\u63a5\u53e3：\u628a in \u548c out \u7528\u5230\u81ea\u5df1\u7684\u8bbe\u8ba1\u91cc<\/li>\n
  • \u59d4\u6258\u4e2d\u7684\u9006\u53d8\u4e0e\u534f\u53d8：\u770b\u61c2 Action \u548c Func<\/li>\n
  • in\u3001out \u4e0d\u53ea\u4e00\u79cd\u542b\u4e49：\u522b\u548c\u53c2\u6570\u5173\u952e\u5b57\u6df7\u6dc6<\/li>\n
  • \u5e38\u89c1\u6cdb\u578b\u63a5\u53e3\u4e0e\u59d4\u6258\u901f\u67e5<\/li>\n
  • \u65b0\u624b\u6700\u5bb9\u6613\u8e29\u7684 6 \u4e2a\u5751<\/li>\n
  • \u5b9e\u6218\u603b\u7ed3：\u4ec0\u4e48\u65f6\u5019\u9700\u8981\u5173\u6ce8\u9006\u53d8\u4e0e\u534f\u53d8<\/li>\n
    \n

    \u4e00\u3001\u4e3a\u4ec0\u4e48\u5b66\u4e86\u7ee7\u627f，\u8fd8\u4f1a\u88ab\u6cdb\u578b\u7c7b\u578b\u8f6c\u6362\u96be\u4f4f<\/h3>\n

    \u5047\u8bbe\u9879\u76ee\u91cc\u6709\u4e00\u4e2a\u57fa\u7c7b Animal，\u8fd8\u6709\u4e24\u4e2a\u6d3e\u751f\u7c7b Dog \u548c Cat：<\/p>\n

    public<\/span> class<\/span> Animal<\/span> {<\/span> }<\/span>
    \npublic<\/span> class<\/span> Dog<\/span> :<\/span> Animal<\/span><\/span> {<\/span> }<\/span>
    \npublic<\/span> class<\/span> Cat<\/span> :<\/span> Animal<\/span><\/span> {<\/span> }<\/span><\/p>\n

    \u56e0\u4e3a Dog \u7ee7\u627f\u81ea Animal，\u6240\u4ee5\u666e\u901a\u7684\u7ee7\u627f\u8f6c\u6362\u5b8c\u5168\u6ca1\u95ee\u9898：<\/p>\n

    Dog<\/span> dog =<\/span> new<\/span> Dog<\/span>(<\/span>)<\/span>;<\/span>
    \nAnimal<\/span> animal =<\/span> dog;<\/span><\/p>\n

    \u8fd9\u5f88\u597d\u7406\u89e3：\u72d7\u662f\u4e00\u79cd\u52a8\u7269，\u56e0\u6b64\u53ef\u4ee5\u628a\u72d7\u5bf9\u8c61\u653e\u5230\u4e00\u4e2a Animal \u7c7b\u578b\u7684\u53d8\u91cf\u4e2d\u3002<\/p>\n

    \u4f46\u5f53\u6cdb\u578b\u51fa\u73b0\u540e，\u60c5\u51b5\u5c31\u4e0d\u4e00\u6837\u4e86：<\/p>\n

    List<<\/span>Dog><\/span><\/span> dogs =<\/span> new<\/span> List<<\/span>Dog><\/span><\/span>(<\/span>)<\/span>;<\/span>
    \n\/\/ List<Animal> animals = dogs; \/\/ \u7f16\u8bd1\u9519\u8bef<\/span><\/p>\n

    \u867d\u7136 Dog \u662f Animal，\u4f46 List<Dog> \u5e76\u4e0d\u662f List<Animal>\u3002\u8fd9\u5f80\u5f80\u8ba9\u521a\u5b66\u5b8c\u7ee7\u627f\u548c\u6cdb\u578b\u7684\u4eba\u611f\u5230\u56f0\u60d1：\u65e2\u7136\u72d7\u662f\u52a8\u7269，\u4e3a\u4ec0\u4e48\u88c5\u72d7\u7684\u5217\u8868\u4e0d\u80fd\u5f53\u6210\u88c5\u52a8\u7269\u7684\u5217\u8868？<\/p>\n

    \u7b54\u6848\u662f：\u6cdb\u578b\u7c7b\u578b\u9ed8\u8ba4\u662f\u4e0d\u53d8\u7684\u3002\u5982\u679c\u7f16\u8bd1\u5668\u5141\u8bb8\u4e0a\u9762\u7684\u8f6c\u6362，\u5c31\u53ef\u80fd\u628a\u4e00\u53ea\u732b\u653e\u8fdb\u539f\u672c\u53ea\u5141\u8bb8\u5b58\u653e\u72d7\u7684\u5217\u8868\u91cc，\u7834\u574f\u7c7b\u578b\u5b89\u5168\u3002<\/p>\n

    C# \u7684\u9006\u53d8\u4e0e\u534f\u53d8，\u5c31\u662f\u5728\u4fdd\u8bc1\u7c7b\u578b\u5b89\u5168\u7684\u524d\u63d0\u4e0b，\u8ba9\u90e8\u5206\u6cdb\u578b\u63a5\u53e3\u548c\u59d4\u6258\u652f\u6301\u66f4\u7075\u6d3b\u7684\u7c7b\u578b\u8f6c\u6362\u3002<\/p>\n

    \u4e8c\u3001\u5148\u641e\u61c2\u4e00\u4e2a\u524d\u63d0：\u6d3e\u751f\u7c7b\u53ef\u4ee5\u5f53\u57fa\u7c7b\u7528<\/h3>\n

    \u4e3a\u4e86\u8bb2\u6e05\u695a\u9006\u53d8\u548c\u534f\u53d8，\u5148\u7edf\u4e00\u672c\u6587\u4f7f\u7528\u7684\u7ee7\u627f\u5173\u7cfb：<\/p>\n

    public<\/span> class<\/span> Animal<\/span>
    \n{<\/span>
    \n public<\/span> string<\/span><\/span> Name {<\/span> get<\/span>;<\/span> set<\/span>;<\/span> }<\/span>
    \n public<\/span> Animal<\/span>(<\/span>string<\/span><\/span> name)<\/span> {<\/span> Name =<\/span> name;<\/span> }<\/span>
    \n}<\/span>
    \npublic<\/span> class<\/span> Dog<\/span> :<\/span> Animal<\/span><\/span>
    \n{<\/span>
    \n public<\/span> Dog<\/span>(<\/span>string<\/span><\/span> name)<\/span> :<\/span> base<\/span>(<\/span>name)<\/span> {<\/span> }<\/span>
    \n}<\/span>
    \npublic<\/span> class<\/span> Cat<\/span> :<\/span> Animal<\/span><\/span>
    \n{<\/span>
    \n public<\/span> Cat<\/span>(<\/span>string<\/span><\/span> name)<\/span> :<\/span> base<\/span>(<\/span>name)<\/span> {<\/span> }<\/span>
    \n}<\/span><\/p>\n

    \u5176\u4e2d，Animal \u662f\u57fa\u7c7b，Dog \u548c Cat \u662f\u6d3e\u751f\u7c7b\u3002\u666e\u901a\u8d4b\u503c\u9075\u5faa\u4e0b\u9762\u7684\u65b9\u5411：<\/p>\n

    Dog<\/span> dog =<\/span> new<\/span> Dog<\/span>(<\/span>"\u65fa\u8d22"<\/span>)<\/span>;<\/span>
    \nAnimal<\/span> animal =<\/span> dog;<\/span> \/\/ \u53ef\u4ee5：Dog \u8f6c\u6210 Animal<\/span><\/p>\n

    \u53ef\u4ee5\u628a\u5b83\u8bb0\u6210：\u5177\u4f53\u7684\u4e1c\u897f，\u53ef\u4ee5\u6309\u66f4\u901a\u7528\u7684\u8eab\u4efd\u6765\u770b\u5f85；\u4f46\u901a\u7528\u7684\u4e1c\u897f，\u4e0d\u4e00\u5b9a\u80fd\u5f53\u6210\u67d0\u4e2a\u5177\u4f53\u7c7b\u578b\u3002 \u4f8b\u5982，\u72d7\u4e00\u5b9a\u662f\u52a8\u7269，\u4f46\u4e00\u53ea\u52a8\u7269\u4e0d\u4e00\u5b9a\u662f\u72d7\u3002<\/p>\n

    \u540e\u9762\u6240\u6709\u7684\u89c4\u5219，\u90fd\u53ef\u4ee5\u56f4\u7ed5\u8fd9\u4e2a\u65b9\u5411\u7406\u89e3：<\/p>\n

      \n
    • \u534f\u53d8： \u4e3b\u8981\u5173\u6ce8\u201c\u63d0\u4f9b\u3001\u8fd4\u56de\u4ec0\u4e48\u201d，\u5141\u8bb8\u628a\u66f4\u5177\u4f53\u7684\u7c7b\u578b\u7ed3\u679c，\u5f53\u6210\u66f4\u901a\u7528\u7684\u7c7b\u578b\u7ed3\u679c\u4f7f\u7528\u3002<\/li>\n
    • \u9006\u53d8： \u4e3b\u8981\u5173\u6ce8\u201c\u63a5\u6536\u3001\u5904\u7406\u4ec0\u4e48\u201d，\u5141\u8bb8\u628a\u80fd\u5904\u7406\u66f4\u901a\u7528\u7c7b\u578b\u7684\u5bf9\u8c61，\u5f53\u6210\u80fd\u5904\u7406\u66f4\u5177\u4f53\u7c7b\u578b\u7684\u5bf9\u8c61\u4f7f\u7528\u3002<\/li>\n<\/ul>\n

      \u4e09\u3001\u4e3a\u4ec0\u4e48 List<Dog> \u4e0d\u80fd\u76f4\u63a5\u5f53\u6210 List<Animal><\/h3>\n

      \u5148\u770b\u4e00\u4e2a\u5bb9\u6613\u8bef\u5224\u7684\u4f8b\u5b50：<\/p>\n

      List<<\/span>Dog><\/span><\/span> dogs =<\/span> new<\/span> List<<\/span>Dog><\/span><\/span>(<\/span>)<\/span>;<\/span>
      \ndogs.<\/span>Add<\/span>(<\/span>new<\/span> Dog<\/span>(<\/span>"\u65fa\u8d22"<\/span>)<\/span>)<\/span>;<\/span>
      \n\/\/ List<Animal> animals = dogs; \/\/ \u7f16\u8bd1\u9519\u8bef<\/span><\/p>\n

      \u95ee\u9898\u5728\u4e8e List<T> \u4e0d\u53ea\u662f\u8bfb\u53d6\u6570\u636e，\u5b83\u8fd8\u53ef\u4ee5\u6dfb\u52a0\u6570\u636e\u3002\u5047\u8bbe\u8fd9\u6b21\u8f6c\u6362\u88ab\u5141\u8bb8，\u4ee3\u7801\u5c31\u53ef\u4ee5\u8fd9\u6837\u5199：<\/p>\n

      \/\/ \u5047\u8bbe\u8fd9\u79cd\u8f6c\u6362\u53ef\u4ee5\u6210\u7acb（\u5b9e\u9645\u4e0a\u4e0d\u80fd\u7f16\u8bd1）<\/span>
      \nList<<\/span>Dog><\/span><\/span> dogs =<\/span> new<\/span> List<<\/span>Dog><\/span><\/span>(<\/span>)<\/span>;<\/span>
      \n\/\/ List<Animal> animals = dogs;<\/span>
      \n\/\/ animals.Add(new Cat("\u5c0f\u82b1"));<\/span><\/p>\n

      \u5982\u679c animals \u771f\u80fd\u5f15\u7528\u540c\u4e00\u4e2a\u53ea\u63a5\u53d7 Dog \u7684\u5217\u8868，\u901a\u8fc7 animals.Add(new Cat(…)) \u5c31\u4f1a\u628a\u732b\u653e\u8fdb\u72d7\u5217\u8868\u4e2d，\u540e\u7eed\u8bfb\u53d6\u65f6\u4fbf\u53ef\u80fd\u51fa\u73b0\u7c7b\u578b\u5b89\u5168\u95ee\u9898\u3002<\/p>\n

      \u56e0\u6b64，List<T> \u7684\u7c7b\u578b\u53c2\u6570 T \u662f\u4e0d\u53d8\u7684（Invariant）：List<Dog> \u4e0d\u4f1a\u56e0\u4e3a Dog \u7ee7\u627f Animal \u5c31\u81ea\u52a8\u53d8\u6210 List<Animal>\u3002<\/p>\n

      \u4f46\u5982\u679c\u53ea\u9700\u8981\u8bfb\u53d6\u6570\u636e，\u53ef\u4ee5\u4f7f\u7528\u652f\u6301\u534f\u53d8\u7684 IEnumerable<T>：<\/p>\n

      List<<\/span>Dog><\/span><\/span> dogs =<\/span> new<\/span> List<<\/span>Dog><\/span><\/span>
      \n{<\/span>
      \n new<\/span> Dog<\/span>(<\/span>"\u65fa\u8d22"<\/span>)<\/span>,<\/span>
      \n new<\/span> Dog<\/span>(<\/span>"\u56e2\u5b50"<\/span>)<\/span>
      \n}<\/span>;<\/span>
      \nIEnumerable<<\/span>Dog><\/span><\/span> dogEnumerable =<\/span> dogs;<\/span>
      \nIEnumerable<<\/span>Animal><\/span><\/span> animalEnumerable =<\/span> dogEnumerable;<\/span>
      \nforeach<\/span> (<\/span>Animal<\/span> animal in<\/span> animalEnumerable)<\/span>
      \n{<\/span>
      \n Console.<\/span>WriteLine<\/span>(<\/span>animal.<\/span>Name)<\/span>;<\/span>
      \n}<\/span><\/p>\n

      \u8f93\u51fa：<\/p>\n

      \u65fa\u8d22
      \n\u56e2\u5b50<\/p>\n

      IEnumerable<out T> \u4e3b\u8981\u7528\u4e8e\u679a\u4e3e\u3001\u8bfb\u53d6\u5143\u7d20，\u4e0d\u63d0\u4f9b\u5411\u5176\u4e2d\u6dfb\u52a0\u5143\u7d20\u7684\u63a5\u53e3\u6210\u5458，\u56e0\u6b64\u53ef\u4ee5\u5b89\u5168\u5730\u628a IEnumerable<Dog> \u5f53\u6210 IEnumerable<Animal> \u4f7f\u7528\u3002\u8fd9\u5c31\u662f\u534f\u53d8\u6700\u5e38\u89c1\u7684\u5e94\u7528\u4e4b\u4e00\u3002<\/p>\n

      \u56db\u3001\u534f\u53d8：out \u8ba9\u201c\u8fd4\u56de\u66f4\u5177\u4f53\u7684\u7c7b\u578b\u201d\u53d8\u5f97\u7075\u6d3b<\/h3>\n

      4.1 \u534f\u53d8\u5230\u5e95\u662f\u4ec0\u4e48<\/h4>\n

      **\u534f\u53d8（Covariance）**\u5141\u8bb8\u6cdb\u578b\u63a5\u53e3\u6216\u59d4\u6258\u7684\u7c7b\u578b\u53c2\u6570，\u6cbf\u7740\u7ee7\u627f\u5173\u7cfb\u4ece\u6d3e\u751f\u7c7b\u578b\u8f6c\u6362\u5230\u57fa\u7c7b\u7c7b\u578b\u3002\u58f0\u660e\u534f\u53d8\u7c7b\u578b\u53c2\u6570\u65f6\u4f7f\u7528 out\u3002<\/p>\n

      \u5148\u8bb0\u4f4f\u4e00\u4e2a\u7b80\u5355\u53e3\u8bc0：\u53ea\u8d1f\u8d23\u63d0\u4f9b\u7ed3\u679c\u65f6，\u901a\u5e38\u53ef\u4ee5\u8003\u8651\u534f\u53d8\u3002<\/p>\n

      \u4f8b\u5982：<\/p>\n

      IEnumerable<<\/span>Dog><\/span><\/span> dogs =<\/span> new<\/span> List<<\/span>Dog><\/span><\/span>(<\/span>)<\/span>;<\/span>
      \nIEnumerable<<\/span>Animal><\/span><\/span> animals =<\/span> dogs;<\/span> \/\/ \u53ef\u4ee5，IEnumerable<T> \u7684 T \u662f\u534f\u53d8\u7684<\/span><\/p>\n

      \u8fd9\u91cc\u7684\u65b9\u5411\u662f\u4ece Dog \u5230 Animal\u3002IEnumerable<Dog> \u63d0\u4f9b\u7684\u6bcf\u4e2a\u5143\u7d20\u90fd\u662f Dog，\u800c\u8c03\u7528\u65b9\u53ea\u8981\u6c42\u5f97\u5230 Animal，\u6240\u4ee5\u628a\u5b83\u5f53\u6210 IEnumerable<Animal> \u4f7f\u7528\u662f\u5b89\u5168\u7684\u3002<\/p>\n

      4.2 \u81ea\u5df1\u58f0\u660e\u4e00\u4e2a\u534f\u53d8\u63a5\u53e3<\/h4>\n

      \u53ef\u4ee5\u4f7f\u7528 out \u58f0\u660e\u4e00\u4e2a\u53ea\u8d1f\u8d23\u8fd4\u56de\u6570\u636e\u7684\u6cdb\u578b\u63a5\u53e3：<\/p>\n

      public<\/span> interface<\/span> IProducer<<\/span>out<\/span> T><\/span><\/span>
      \n{<\/span>
      \n T<\/span> Get<\/span>(<\/span>)<\/span>;<\/span>
      \n}<\/span>
      \npublic<\/span> class<\/span> DogProducer<\/span> :<\/span> IProducer<<\/span>Dog><\/span><\/span><\/span>
      \n{<\/span>
      \n public<\/span> Dog<\/span> Get<\/span>(<\/span>)<\/span> =><\/span> new<\/span> Dog<\/span>(<\/span>"\u65fa\u8d22"<\/span>)<\/span>;<\/span>
      \n}<\/span><\/p>\n

      \u4f7f\u7528\u65f6：<\/p>\n

      IProducer<<\/span>Dog><\/span><\/span> dogProducer =<\/span> new<\/span> DogProducer<\/span>(<\/span>)<\/span>;<\/span>
      \nIProducer<<\/span>Animal><\/span><\/span> animalProducer =<\/span> dogProducer;<\/span>
      \nAnimal<\/span> animal =<\/span> animalProducer.<\/span>Get<\/span>(<\/span>)<\/span>;<\/span>
      \nConsole.<\/span>WriteLine<\/span>(<\/span>animal.<\/span>Name)<\/span>;<\/span><\/p>\n

      \u8f93\u51fa：<\/p>\n

      \u65fa\u8d22<\/p>\n

      DogProducer \u751f\u4ea7\u7684\u662f\u72d7，\u4f46\u63a5\u53e3\u8c03\u7528\u65b9\u53ea\u9700\u8981\u4e00\u4e2a\u52a8\u7269，\u56e0\u6b64\u53ef\u4ee5\u628a IProducer<Dog> \u8f6c\u6362\u6210 IProducer<Animal>\u3002<\/p>\n

      4.3 \u4e3a\u4ec0\u4e48 out T \u4e0d\u80fd\u968f\u4fbf\u7528<\/h4>\n

      \u534f\u53d8\u7c7b\u578b\u53c2\u6570 T \u53ef\u4ee5\u7528\u5728\u63a5\u53e3\u6210\u5458\u7684\u8fd4\u56de\u4f4d\u7f6e，\u4f46\u4e0d\u80fd\u76f4\u63a5\u7528\u4f5c\u666e\u901a\u8f93\u5165\u53c2\u6570\u7684\u7c7b\u578b：<\/p>\n

      public<\/span> interface<\/span> IProducer<<\/span>out<\/span> T><\/span><\/span>
      \n{<\/span>
      \n T<\/span> Get<\/span>(<\/span>)<\/span>;<\/span>
      \n \/\/ void Add(T item); \/\/ \u7f16\u8bd1\u9519\u8bef：\u534f\u53d8\u7684 T \u4e0d\u80fd\u4f5c\u4e3a\u8f93\u5165\u53c2\u6570\u7c7b\u578b<\/span>
      \n}<\/span><\/p>\n

      \u539f\u56e0\u5e76\u4e0d\u590d\u6742：\u5047\u8bbe IProducer<Dog> \u53ef\u4ee5\u8f6c\u6210 IProducer<Animal>，\u5982\u679c\u8fd9\u4e2a\u63a5\u53e3\u8fd8\u5141\u8bb8\u8c03\u7528\u65b9\u6dfb\u52a0\u4efb\u610f Animal，\u5c31\u53ef\u80fd\u628a Cat \u585e\u7ed9\u53ea\u9002\u5408\u5904\u7406 Dog \u7684\u5b9e\u73b0\u3002\u9650\u5236 out T \u53ea\u80fd\u51fa\u73b0\u5728\u5141\u8bb8\u7684\u4f4d\u7f6e，\u662f\u4e3a\u4e86\u4fdd\u8bc1\u7c7b\u578b\u5b89\u5168\u3002<\/p>\n

      \u7406\u89e3\u91cd\u70b9： out \u5728\u6cdb\u578b\u63a5\u53e3\u548c\u59d4\u6258\u7684\u58f0\u660e\u4e2d\u8868\u793a\u201c\u534f\u53d8\u201d，\u91cd\u70b9\u662f\u7c7b\u578b\u53c2\u6570\u53ef\u4ee5\u51fa\u73b0\u5728\u8f93\u51fa\u4f4d\u7f6e；\u5b83\u4e0d\u662f\u8bf4\u8fd9\u4e2a\u63a5\u53e3\u4e00\u5b9a\u8981\u6709\u4e00\u4e2a\u540d\u4e3a out \u7684\u53c2\u6570\u3002<\/p>\n

      \u4e94\u3001\u9006\u53d8：in \u8ba9\u201c\u63a5\u6536\u66f4\u901a\u7528\u7684\u7c7b\u578b\u201d\u4e5f\u80fd\u5904\u7406\u5177\u4f53\u5bf9\u8c61<\/h3>\n

      5.1 \u9006\u53d8\u5230\u5e95\u662f\u4ec0\u4e48<\/h4>\n

      **\u9006\u53d8（Contravariance）**\u5141\u8bb8\u6cdb\u578b\u63a5\u53e3\u6216\u59d4\u6258\u7684\u7c7b\u578b\u53c2\u6570，\u6cbf\u7740\u7ee7\u627f\u5173\u7cfb\u4ece\u57fa\u7c7b\u65b9\u5411\u7528\u4e8e\u6d3e\u751f\u7c7b\u7c7b\u578b\u53c2\u6570\u3002\u58f0\u660e\u9006\u53d8\u7c7b\u578b\u53c2\u6570\u65f6\u4f7f\u7528 in\u3002<\/p>\n

      \u53ef\u4ee5\u8fd9\u6837\u7406\u89e3：\u80fd\u5904\u7406\u6240\u6709\u52a8\u7269\u7684\u5de5\u5177，\u5f53\u7136\u4e5f\u80fd\u5904\u7406\u72d7\u3002 \u4f46\u53ea\u4f1a\u5904\u7406\u72d7\u7684\u5de5\u5177，\u4e0d\u4e00\u5b9a\u80fd\u5904\u7406\u732b\u3002<\/p>\n

      \u5047\u8bbe\u6709\u4e00\u4e2a\u63a5\u53e3，\u4e13\u95e8\u7528\u4e8e\u63a5\u6536\u5e76\u5904\u7406\u6570\u636e：<\/p>\n

      public<\/span> interface<\/span> IConsumer<<\/span>in<\/span> T><\/span><\/span>
      \n{<\/span>
      \n void<\/span><\/span> Consume<\/span>(<\/span>T<\/span> item)<\/span>;<\/span>
      \n}<\/span>
      \npublic<\/span> class<\/span> AnimalPrinter<\/span> :<\/span> IConsumer<<\/span>Animal><\/span><\/span><\/span>
      \n{<\/span>
      \n public<\/span> void<\/span><\/span> Consume<\/span>(<\/span>Animal<\/span> animal)<\/span>
      \n {<\/span>
      \n Console.<\/span>WriteLine<\/span>(<\/span>$"\u6536\u5230\u52a8\u7269：<\/span>{<\/span>animal.<\/span>Name<\/span>}<\/span><\/span>"<\/span><\/span>)<\/span>;<\/span>
      \n }<\/span>
      \n}<\/span><\/p>\n

      AnimalPrinter \u53ef\u4ee5\u5904\u7406\u4efb\u4f55 Animal，\u81ea\u7136\u4e5f\u53ef\u4ee5\u5904\u7406 Dog\u3002\u6240\u4ee5\u53ef\u4ee5\u8fd9\u6837\u8d4b\u503c：<\/p>\n

      IConsumer<<\/span>Animal><\/span><\/span> animalConsumer =<\/span> new<\/span> AnimalPrinter<\/span>(<\/span>)<\/span>;<\/span>
      \nIConsumer<<\/span>Dog><\/span><\/span> dogConsumer =<\/span> animalConsumer;<\/span>
      \ndogConsumer.<\/span>Consume<\/span>(<\/span>new<\/span> Dog<\/span>(<\/span>"\u65fa\u8d22"<\/span>)<\/span>)<\/span>;<\/span><\/p>\n

      \u8f93\u51fa：<\/p>\n

      \u6536\u5230\u52a8\u7269：\u65fa\u8d22<\/p>\n

      \u6ce8\u610f\u8f6c\u6362\u65b9\u5411：\u8fd9\u91cc\u662f IConsumer<Animal> \u8f6c\u6210 IConsumer<Dog>，\u548c\u534f\u53d8\u6b63\u597d\u76f8\u53cd\u3002\u56e0\u4e3a\u8fd9\u4e2a\u6d88\u8d39\u8005\u80fd\u5904\u7406\u66f4\u5e7f\u6cdb\u7684\u52a8\u7269\u7c7b\u578b，\u6240\u4ee5\u628a\u5b83\u5f53\u6210\u4e00\u4e2a\u4e13\u95e8\u63a5\u6536\u72d7\u7684\u6d88\u8d39\u8005\u4f7f\u7528\u662f\u5b89\u5168\u7684\u3002<\/p>\n

      5.2 \u4e3a\u4ec0\u4e48 in T \u9002\u5408\u8f93\u5165\u4f4d\u7f6e<\/h4>\n

      \u9006\u53d8\u7c7b\u578b\u53c2\u6570 T \u53ef\u4ee5\u7528\u5728\u63a5\u53e3\u6210\u5458\u7684\u8f93\u5165\u53c2\u6570\u4f4d\u7f6e：<\/p>\n

      public<\/span> interface<\/span> IConsumer<<\/span>in<\/span> T><\/span><\/span>
      \n{<\/span>
      \n void<\/span><\/span> Consume<\/span>(<\/span>T<\/span> item)<\/span>;<\/span>
      \n \/\/ T Get(); \/\/ \u7f16\u8bd1\u9519\u8bef：\u9006\u53d8\u7684 T \u4e0d\u80fd\u76f4\u63a5\u4f5c\u4e3a\u8fd4\u56de\u7c7b\u578b<\/span>
      \n}<\/span><\/p>\n

      \u5982\u679c\u4e00\u4e2a\u53ea\u63a5\u6536 Dog \u7684\u53d8\u91cf\u5b9e\u9645\u6307\u5411 IConsumer<Animal>，\u8c03\u7528\u65b9\u4f20\u5165\u72d7\u6ca1\u6709\u95ee\u9898，\u56e0\u4e3a\u72d7\u5c31\u662f\u52a8\u7269\u3002\u53cd\u8fc7\u6765，\u5982\u679c\u53ea\u63a5\u6536\u72d7\u7684\u5bf9\u8c61\u88ab\u5f53\u4f5c\u53ef\u4ee5\u5904\u7406\u4efb\u610f\u52a8\u7269\u7684\u5bf9\u8c61，\u5c31\u53ef\u80fd\u4f20\u5165\u732b\u800c\u51fa\u9519\u3002\u56e0\u6b64\u9006\u53d8\u7684\u8f6c\u6362\u65b9\u5411\u5fc5\u987b\u662f\u8fd9\u6837\u8bbe\u8ba1\u7684\u3002<\/p>\n

      \u516d\u3001\u81ea\u5b9a\u4e49\u6cdb\u578b\u63a5\u53e3：\u628a in \u548c out \u7528\u5230\u81ea\u5df1\u7684\u8bbe\u8ba1\u91cc<\/h3>\n

      \u5b9e\u9645\u9879\u76ee\u4e2d，\u53ef\u4ee5\u6839\u636e\u63a5\u53e3\u627f\u62c5\u7684\u804c\u8d23\u51b3\u5b9a\u662f\u5426\u58f0\u660e\u9006\u53d8\u6216\u534f\u53d8\u3002<\/p>\n

      6.1 \u53ea\u63d0\u4f9b\u7ed3\u679c：\u8003\u8651 out<\/h4>\n

      \u4f8b\u5982，\u89c6\u89c9\u68c0\u6d4b\u7cfb\u7edf\u4e2d\u6709\u4e00\u4e2a\u7ed3\u679c\u8bfb\u53d6\u63a5\u53e3：<\/p>\n

      public<\/span> interface<\/span> IResultProvider<<\/span>out<\/span> T><\/span><\/span>
      \n{<\/span>
      \n T<\/span> GetResult<\/span>(<\/span>)<\/span>;<\/span>
      \n}<\/span><\/p>\n

      \u5982\u679c\u67d0\u4e2a\u5b9e\u73b0\u63d0\u4f9b CircleResult，\u800c\u8c03\u7528\u65b9\u53ea\u5173\u5fc3\u66f4\u901a\u7528\u7684 ShapeResult，\u534f\u53d8\u5c31\u80fd\u8ba9\u5b83\u4eec\u66f4\u5bb9\u6613\u914d\u5408\u4f7f\u7528\u3002\u524d\u63d0\u662f CircleResult \u786e\u5b9e\u7ee7\u627f\u81ea ShapeResult，\u5e76\u4e14\u63a5\u53e3\u8bbe\u8ba1\u7b26\u5408\u534f\u53d8\u7684\u8f93\u51fa\u89c4\u5219\u3002<\/p>\n

      6.2 \u53ea\u63a5\u6536\u6570\u636e：\u8003\u8651 in<\/h4>\n

      \u4f8b\u5982，\u7ed9\u68c0\u6d4b\u7ed3\u679c\u5199\u65e5\u5fd7\u3001\u8f93\u51fa\u62a5\u544a\u6216\u6267\u884c\u7edf\u4e00\u5904\u7406：<\/p>\n

      public<\/span> interface<\/span> IResultHandler<<\/span>in<\/span> T><\/span><\/span>
      \n{<\/span>
      \n void<\/span><\/span> Handle<\/span>(<\/span>T<\/span> result)<\/span>;<\/span>
      \n}<\/span><\/p>\n

      \u4e00\u4e2a\u80fd\u5904\u7406\u6240\u6709 ShapeResult \u7684\u5904\u7406\u5668，\u4e5f\u53ef\u4ee5\u63a5\u6536\u66f4\u5177\u4f53\u7684 CircleResult\u3002\u8fd9\u6837\u7684\u8bbe\u8ba1\u80fd\u51cf\u5c11\u4e0d\u5fc5\u8981\u7684\u7c7b\u578b\u9002\u914d\u4ee3\u7801\u3002<\/p>\n

      6.3 \u540c\u65f6\u8f93\u5165\u548c\u8f93\u51fa\u65f6，\u901a\u5e38\u4e0d\u80fd\u6807\u8bb0\u4e3a\u53d8\u4f53<\/h4>\n

      \u5982\u679c\u540c\u4e00\u4e2a\u7c7b\u578b\u53c2\u6570\u65e2\u8981\u4f5c\u4e3a\u8f93\u5165，\u53c8\u8981\u4f5c\u4e3a\u8f93\u51fa，\u4e00\u822c\u4e0d\u80fd\u76f4\u63a5\u58f0\u660e\u4e3a in \u6216 out：<\/p>\n

      public<\/span> interface<\/span> IRepository<<\/span>T><\/span><\/span>
      \n{<\/span>
      \n T<\/span> GetById<\/span>(<\/span>int<\/span><\/span> id)<\/span>;<\/span>
      \n void<\/span><\/span> Save<\/span>(<\/span>T<\/span> item)<\/span>;<\/span>
      \n}<\/span><\/p>\n

      T \u65e2\u51fa\u73b0\u5728 GetById \u7684\u8fd4\u56de\u4f4d\u7f6e，\u4e5f\u51fa\u73b0\u5728 Save \u7684\u53c2\u6570\u4f4d\u7f6e，\u6240\u4ee5\u6b64\u5904\u5e94\u4fdd\u6301\u4e0d\u53d8\u3002\u8fd9\u4e2a\u8bbe\u8ba1\u5e76\u4e0d\u662f\u9519\u8bef，\u800c\u662f\u5b83\u7684\u804c\u8d23\u51b3\u5b9a\u4e86\u5b83\u9700\u8981\u540c\u65f6\u8bfb\u53d6\u548c\u63a5\u6536 T\u3002<\/p>\n

      \u9700\u8981\u6ce8\u610f：in \u548c out \u53ea\u80fd\u7528\u4e8e\u6cdb\u578b\u63a5\u53e3\u3001\u6cdb\u578b\u59d4\u6258\u7684\u7c7b\u578b\u53c2\u6570\u58f0\u660e，\u4e0d\u80fd\u7528\u4e8e\u7ed9\u666e\u901a\u6cdb\u578b\u7c7b\u6216\u6cdb\u578b\u7ed3\u6784\u4f53\u58f0\u660e\u53d8\u4f53\u7c7b\u578b\u53c2\u6570\u3002\u4f8b\u5982，\u4e0d\u80fd\u5199\u6210 class Box<out T>\u3002<\/p>\n

      \u4e03\u3001\u59d4\u6258\u4e2d\u7684\u9006\u53d8\u4e0e\u534f\u53d8：\u770b\u61c2 Action \u548c Func<\/h3>\n

      \u9006\u53d8\u548c\u534f\u53d8\u4e0d\u4ec5\u7528\u4e8e\u6cdb\u578b\u63a5\u53e3，\u4e5f\u5927\u91cf\u51fa\u73b0\u5728 C# \u5185\u7f6e\u59d4\u6258\u4e2d\u3002\u5e73\u65f6\u7ecf\u5e38\u4f7f\u7528\u7684 Action<T> \u548c Func<T, TResult>，\u5c31\u5df2\u7ecf\u5b9a\u4e49\u597d\u4e86\u5bf9\u5e94\u89c4\u5219\u3002<\/p>\n

      7.1 Action<T>：\u53c2\u6570\u4f4d\u7f6e\u652f\u6301\u9006\u53d8<\/h4>\n

      Action<T> \u8868\u793a\u4e00\u4e2a\u63a5\u6536\u53c2\u6570\u3001\u6ca1\u6709\u8fd4\u56de\u503c\u7684\u59d4\u6258\u3002\u5b83\u7684\u7c7b\u578b\u53c2\u6570\u662f\u9006\u53d8\u7684，\u56e0\u6b64 Action<Animal> \u53ef\u4ee5\u8d4b\u503c\u7ed9 Action<Dog>：<\/p>\n

      Action<<\/span>Animal><\/span><\/span> printAnimal =<\/span> animal =><\/span> Console.<\/span>WriteLine<\/span>(<\/span>animal.<\/span>Name)<\/span>;<\/span>
      \nAction<<\/span>Dog><\/span><\/span> printDog =<\/span> printAnimal;<\/span>
      \nprintDog<\/span>(<\/span>new<\/span> Dog<\/span>(<\/span>"\u65fa\u8d22"<\/span>)<\/span>)<\/span>;<\/span><\/p>\n

      \u8f93\u51fa：<\/p>\n

      \u65fa\u8d22<\/p>\n

      \u539f\u56e0\u662f printAnimal \u672c\u6765\u5c31\u80fd\u63a5\u6536\u4efb\u4f55\u52a8\u7269，\u63a5\u6536\u72d7\u5f53\u7136\u6ca1\u6709\u95ee\u9898\u3002<\/p>\n

      7.2 Func<T, TResult>：\u8f93\u5165\u9006\u53d8，\u8f93\u51fa\u534f\u53d8<\/h4>\n

      Func<T, TResult> \u7684\u7b2c\u4e00\u4e2a\u7c7b\u578b\u53c2\u6570\u7528\u4e8e\u8f93\u5165，\u652f\u6301\u9006\u53d8；\u6700\u540e\u4e00\u4e2a\u7c7b\u578b\u53c2\u6570\u7528\u4e8e\u8fd4\u56de\u7ed3\u679c，\u652f\u6301\u534f\u53d8\u3002<\/p>\n

      Func<<\/span>Animal,<\/span> string<\/span>><\/span><\/span> describeAnimal =<\/span> animal =><\/span> animal.<\/span>Name;<\/span>
      \nFunc<<\/span>Dog,<\/span> object<\/span>><\/span><\/span> describeDog =<\/span> describeAnimal;<\/span>
      \nobject<\/span><\/span> result =<\/span> describeDog<\/span>(<\/span>new<\/span> Dog<\/span>(<\/span>"\u56e2\u5b50"<\/span>)<\/span>)<\/span>;<\/span>
      \nConsole.<\/span>WriteLine<\/span>(<\/span>result)<\/span>;<\/span><\/p>\n

      \u8f93\u51fa：<\/p>\n

      \u56e2\u5b50<\/p>\n

      \u8fd9\u6bb5\u4ee3\u7801\u540c\u65f6\u4f7f\u7528\u4e86\u4e24\u79cd\u53d8\u4f53\u89c4\u5219：<\/p>\n

        \n
      • \u8f93\u5165\u7c7b\u578b\u4ece Animal \u53d8\u6210 Dog，\u5c5e\u4e8e\u9006\u53d8\u3002\u539f\u65b9\u6cd5\u80fd\u63a5\u6536\u6240\u6709\u52a8\u7269，\u56e0\u6b64\u63a5\u6536\u72d7\u6ca1\u6709\u95ee\u9898\u3002<\/li>\n
      • \u8fd4\u56de\u7c7b\u578b\u4ece string \u53d8\u6210 object，\u5c5e\u4e8e\u534f\u53d8\u3002string \u53ef\u4ee5\u5411\u4e0a\u8f6c\u6362\u4e3a object，\u6240\u4ee5\u8c03\u7528\u65b9\u628a\u7ed3\u679c\u5f53\u4f5c object \u63a5\u6536\u662f\u5b89\u5168\u7684\u3002<\/li>\n<\/ul>\n

        7.3 \u65b9\u6cd5\u7ec4\u4e5f\u53ef\u4ee5\u4f53\u73b0\u53d8\u4f53\u8f6c\u6362<\/h4>\n

        \u534f\u53d8\u548c\u9006\u53d8\u4e0d\u53ea\u5b58\u5728\u4e8e\u6cdb\u578b\u7c7b\u578b\u4e4b\u95f4，\u5728\u59d4\u6258\u7ed1\u5b9a\u65b9\u6cd5\u65f6\u4e5f\u80fd\u89c1\u5230\u76f8\u4f3c\u89c4\u5219：<\/p>\n

        static<\/span> string<\/span><\/span> GetName<\/span>(<\/span>)<\/span> =><\/span> "\u65fa\u8d22"<\/span>;<\/span>
        \nstatic<\/span> void<\/span><\/span> PrintObject<\/span>(<\/span>object<\/span><\/span> value<\/span>)<\/span> =><\/span> Console.<\/span>WriteLine<\/span>(<\/span>value<\/span>)<\/span>;<\/span>
        \nFunc<<\/span>object<\/span>><\/span><\/span> getObject =<\/span> GetName;<\/span>
        \nAction<<\/span>string<\/span>><\/span><\/span> printString =<\/span> PrintObject;<\/span>
        \nConsole.<\/span>WriteLine<\/span>(<\/span>getObject<\/span>(<\/span>)<\/span>)<\/span>;<\/span>
        \nprintString<\/span>(<\/span>"Hello C#"<\/span>)<\/span>;<\/span><\/p>\n

        GetName \u8fd4\u56de string，\u800c\u59d4\u6258\u5141\u8bb8\u8fd4\u56de object；PrintObject \u63a5\u6536 object，\u800c Action<string> \u53ea\u4f1a\u4f20\u5165\u5b57\u7b26\u4e32\u3002\u8fd9\u4e24\u79cd\u8c03\u7528\u90fd\u662f\u5b89\u5168\u7684\u3002<\/p>\n

        \u516b\u3001in\u3001out \u4e0d\u53ea\u4e00\u79cd\u542b\u4e49：\u522b\u548c\u53c2\u6570\u5173\u952e\u5b57\u6df7\u6dc6<\/h3>\n

        \u8fd9\u662f C# \u5b66\u4e60\u4e2d\u5f88\u5bb9\u6613\u6df7\u6dc6\u7684\u5730\u65b9：in \u548c out \u65e2\u80fd\u51fa\u73b0\u5728\u6cdb\u578b\u7c7b\u578b\u53c2\u6570\u58f0\u660e\u4e2d，\u4e5f\u80fd\u4f5c\u4e3a\u65b9\u6cd5\u53c2\u6570\u7684\u5173\u952e\u5b57，\u4f46\u5b83\u4eec\u8868\u8fbe\u7684\u4e0d\u662f\u540c\u4e00\u4ef6\u4e8b\u3002<\/p>\n\n\u5199\u6cd5\u6240\u5728\u4f4d\u7f6e\u542b\u4e49<\/tr>\n\n\n\n\n\n
        IEnumerable<out T><\/td>\n\u6cdb\u578b\u63a5\u53e3\u58f0\u660e<\/td>\nout \u8868\u793a\u534f\u53d8，\u9650\u5236\u7c7b\u578b\u53c2\u6570\u7684\u4f7f\u7528\u4f4d\u7f6e<\/td>\n<\/tr>\n
        IConsumer<in T><\/td>\n\u6cdb\u578b\u63a5\u53e3\u58f0\u660e<\/td>\nin \u8868\u793a\u9006\u53d8，\u9650\u5236\u7c7b\u578b\u53c2\u6570\u7684\u4f7f\u7528\u4f4d\u7f6e<\/td>\n<\/tr>\n
        void Read(in int value)<\/td>\n\u65b9\u6cd5\u53c2\u6570\u5217\u8868<\/td>\n\u53c2\u6570\u4ee5\u53ea\u8bfb\u5f15\u7528\u65b9\u5f0f\u4f20\u9012，\u8c03\u7528\u65b9\u7684\u503c\u4e0d\u80fd\u901a\u8fc7\u8be5\u53c2\u6570\u88ab\u4fee\u6539<\/td>\n<\/tr>\n
        bool TryGet(out int value)<\/td>\n\u65b9\u6cd5\u53c2\u6570\u5217\u8868<\/td>\n\u65b9\u6cd5\u901a\u8fc7 out \u53c2\u6570\u5411\u8c03\u7528\u65b9\u5199\u5165\u7ed3\u679c，\u8c03\u7528\u524d\u4e0d\u8981\u6c42\u53d8\u91cf\u5df2\u8d4b\u503c<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

        \u56e0\u6b64，\u6cdb\u578b\u58f0\u660e\u4e2d\u7684 out \u4e0d\u662f\u201c\u65b9\u6cd5\u8fd4\u56de\u503c\u201d，\u6cdb\u578b\u58f0\u660e\u4e2d\u7684 in \u4e5f\u4e0d\u662f\u201c\u53ea\u8bfb\u5f15\u7528\u53c2\u6570\u201d\u3002\u5224\u65ad\u542b\u4e49\u65f6，\u5148\u770b\u5173\u952e\u5b57\u51fa\u73b0\u5728\u54ea\u4e2a\u4f4d\u7f6e\u3002<\/p>\n

        \u4e5d\u3001\u5e38\u89c1\u6cdb\u578b\u63a5\u53e3\u4e0e\u59d4\u6258\u901f\u67e5<\/h3>\n

        .NET \u4e2d\u5df2\u7ecf\u6709\u8bb8\u591a\u5b9a\u4e49\u597d\u53d8\u4f53\u89c4\u5219\u7684\u63a5\u53e3\u548c\u59d4\u6258，\u53ef\u4ee5\u76f4\u63a5\u4f7f\u7528，\u4e0d\u9700\u8981\u81ea\u5df1\u91cd\u65b0\u58f0\u660e\u3002<\/p>\n\n\u7c7b\u578b\u53d8\u4f53\u89c4\u5219\u901a\u4fd7\u7406\u89e3<\/tr>\n\n\n\n\n\n\n\n\n\n
        IEnumerable<out T><\/td>\n\u534f\u53d8<\/td>\n\u679a\u4e3e\u8bfb\u53d6\u5143\u7d20，IEnumerable<Dog> \u53ef\u4ee5\u5f53\u6210 IEnumerable<Animal><\/td>\n<\/tr>\n
        IReadOnlyList<out T><\/td>\n\u534f\u53d8<\/td>\n\u901a\u8fc7\u53ea\u8bfb\u5217\u8868\u8bfb\u53d6\u5143\u7d20，\u652f\u6301\u534f\u53d8\u8f6c\u6362<\/td>\n<\/tr>\n
        IEnumerator<out T><\/td>\n\u534f\u53d8<\/td>\n\u901a\u8fc7\u679a\u4e3e\u5668\u8bfb\u53d6\u5143\u7d20<\/td>\n<\/tr>\n
        IComparer<in T><\/td>\n\u9006\u53d8<\/td>\n\u80fd\u6bd4\u8f83\u66f4\u901a\u7528\u7684\u7c7b\u578b，\u4e5f\u80fd\u7528\u4e8e\u6bd4\u8f83\u6d3e\u751f\u7c7b\u578b<\/td>\n<\/tr>\n
        IEqualityComparer<in T><\/td>\n\u9006\u53d8<\/td>\n\u80fd\u5224\u65ad\u57fa\u7c7b\u5bf9\u8c61\u662f\u5426\u76f8\u7b49，\u4e5f\u53ef\u7528\u4e8e\u6d3e\u751f\u7c7b\u578b<\/td>\n<\/tr>\n
        Action<in T><\/td>\n\u9006\u53d8<\/td>\n\u65b9\u6cd5\u63a5\u6536\u53c2\u6570\u3001\u4e0d\u8fd4\u56de\u7ed3\u679c<\/td>\n<\/tr>\n
        Func<in T, out TResult><\/td>\n\u8f93\u5165\u9006\u53d8\u3001\u8fd4\u56de\u534f\u53d8<\/td>\n\u8f93\u5165\u548c\u8fd4\u56de\u7c7b\u578b\u5206\u522b\u6309\u5404\u81ea\u89c4\u5219\u8f6c\u6362<\/td>\n<\/tr>\n
        List<T><\/td>\n\u4e0d\u53d8<\/td>\n\u53ef\u8bfb\u53ef\u5199，\u4e0d\u80fd\u76f4\u63a5\u5c06 List<Dog> \u8d4b\u503c\u7ed9 List<Animal><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

        \u8bb0\u4f4f：\u4e0d\u662f\u6240\u6709\u6cdb\u578b\u90fd\u652f\u6301\u9006\u53d8\u6216\u534f\u53d8\u3002\u5fc5\u987b\u770b\u8fd9\u4e2a\u6cdb\u578b\u7c7b\u578b\u672c\u8eab\u6709\u6ca1\u6709\u58f0\u660e\u76f8\u5e94\u7684\u53d8\u4f53\u89c4\u5219\u3002<\/p>\n

        \u5341\u3001\u65b0\u624b\u6700\u5bb9\u6613\u8e29\u7684 6 \u4e2a\u5751<\/h3>\n

        \u5751 1：\u4ee5\u4e3a\u7ee7\u627f\u5173\u7cfb\u4f1a\u81ea\u52a8\u4f20\u9012\u5230\u6240\u6709\u6cdb\u578b\u7c7b\u578b<\/h4>\n

        Dog \u7ee7\u627f Animal，\u5e76\u4e0d\u4ee3\u8868 List<Dog> \u7ee7\u627f List<Animal>\u3002\u53ea\u6709\u58f0\u660e\u4e3a\u534f\u53d8\u6216\u9006\u53d8\u7684\u6cdb\u578b\u63a5\u53e3\u4e0e\u59d4\u6258，\u624d\u80fd\u6309\u89c4\u5219\u8fdb\u884c\u5bf9\u5e94\u7684\u7c7b\u578b\u8f6c\u6362\u3002<\/p>\n

        \u5751 2：\u628a\u534f\u53d8\u548c\u9006\u53d8\u7684\u65b9\u5411\u8bb0\u53cd<\/h4>\n

        \u8bb0\u4f4f\u4e24\u4e2a\u6700\u5e38\u89c1\u7684\u4f8b\u5b50：<\/p>\n

        IEnumerable<<\/span>Dog><\/span><\/span> dogs =<\/span> new<\/span> List<<\/span>Dog><\/span><\/span>(<\/span>)<\/span>;<\/span>
        \nIEnumerable<<\/span>Animal><\/span><\/span> animals =<\/span> dogs;<\/span> \/\/ \u534f\u53d8：Dog -> Animal<\/span>
        \nAction<<\/span>Animal><\/span><\/span> handleAnimal =<\/span> animal =><\/span> Console.<\/span>WriteLine<\/span>(<\/span>animal.<\/span>Name)<\/span>;<\/span>
        \nAction<<\/span>Dog><\/span><\/span> handleDog =<\/span> handleAnimal;<\/span> \/\/ \u9006\u53d8：Action<Animal> -> Action<Dog><\/span><\/p>\n

        \u534f\u53d8\u5173\u6ce8\u8f93\u51fa，\u901a\u5e38\u4ece\u66f4\u5177\u4f53\u7684\u7c7b\u578b\u5230\u66f4\u901a\u7528\u7684\u7c7b\u578b；\u9006\u53d8\u5173\u6ce8\u8f93\u5165，\u8f6c\u6362\u65b9\u5411\u770b\u8d77\u6765\u76f8\u53cd\u3002<\/p>\n

        \u5751 3：\u8ba4\u4e3a List<T> \u4e5f\u53ef\u4ee5\u76f4\u63a5\u53d8\u4f53\u8f6c\u6362<\/h4>\n

        List<T> \u63d0\u4f9b\u6dfb\u52a0\u548c\u8bfb\u53d6\u7b49\u64cd\u4f5c，\u7c7b\u578b\u53c2\u6570\u662f\u4e0d\u53d8\u7684\u3002\u9700\u8981\u53ea\u8bfb\u8bbf\u95ee\u65f6，\u53ef\u4ee5\u8003\u8651\u4f7f\u7528 IEnumerable<T> \u6216 IReadOnlyList<T> \u8fd9\u6837\u7684\u63a5\u53e3\u3002<\/p>\n

        \u5751 4：\u628a in\u3001out \u5f53\u6210\u80fd\u968f\u5904\u6dfb\u52a0\u7684\u4fee\u9970\u7b26<\/h4>\n

        \u53ea\u80fd\u5728\u652f\u6301\u53d8\u4f53\u7684\u6cdb\u578b\u63a5\u53e3\u548c\u6cdb\u578b\u59d4\u6258\u7684\u7c7b\u578b\u53c2\u6570\u58f0\u660e\u4e2d\u4f7f\u7528\u534f\u53d8\u3001\u9006\u53d8\u58f0\u660e\u3002\u666e\u901a\u6cdb\u578b\u7c7b\u548c\u7ed3\u6784\u4f53\u4e0d\u80fd\u76f4\u63a5\u58f0\u660e class Box<out T> \u6216 struct Box<in T>\u3002<\/p>\n

        \u5751 5：\u8ba4\u4e3a\u503c\u7c7b\u578b\u4e5f\u80fd\u50cf\u5f15\u7528\u7c7b\u578b\u4e00\u6837\u4f7f\u7528\u53d8\u4f53<\/h4>\n

        \u6cdb\u578b\u53d8\u4f53\u8f6c\u6362\u9002\u7528\u4e8e\u5f15\u7528\u7c7b\u578b\u7684\u7c7b\u578b\u53c2\u6570\u3002\u4f8b\u5982，IEnumerable<Dog> \u53ef\u4ee5\u8f6c\u6362\u6210 IEnumerable<Animal>，\u4f46 IEnumerable<int> \u4e0d\u80fd\u56e0\u6b64\u8f6c\u6362\u6210 IEnumerable<object>\u3002\u503c\u7c7b\u578b\u7684\u88c5\u7bb1\u8f6c\u6362\u4e0d\u4f1a\u8ba9\u6cdb\u578b\u63a5\u53e3\u81ea\u52a8\u83b7\u5f97\u534f\u53d8\u80fd\u529b\u3002<\/p>\n

        \u5751 6：\u628a\u201c\u80fd\u8d4b\u503c\u201d\u7406\u89e3\u6210\u201c\u539f\u6765\u7684\u5bf9\u8c61\u7c7b\u578b\u53d8\u4e86\u201d<\/h4>\n

        \u53d8\u4f53\u4e0d\u4f1a\u628a Dog \u5bf9\u8c61\u53d8\u6210 Animal \u5bf9\u8c61，\u4e5f\u4e0d\u4f1a\u4fee\u6539\u5217\u8868\u5185\u90e8\u7684\u6570\u636e\u3002\u5b83\u53ea\u662f\u5141\u8bb8\u4f60\u901a\u8fc7\u4e00\u4e2a\u66f4\u901a\u7528\u6216\u7b26\u5408\u89c4\u5219\u7684\u63a5\u53e3\u3001\u59d4\u6258\u7c7b\u578b\u6765\u4f7f\u7528\u539f\u6709\u5bf9\u8c61，\u5e76\u4e14\u4ecd\u7136\u7531\u7c7b\u578b\u7cfb\u7edf\u4fdd\u8bc1\u5b89\u5168\u3002<\/p>\n

        \u5341\u4e00\u3001\u5b9e\u6218\u603b\u7ed3：\u4ec0\u4e48\u65f6\u5019\u9700\u8981\u5173\u6ce8\u9006\u53d8\u4e0e\u534f\u53d8<\/h3>\n

        \u5f00\u53d1\u65f6\u4e0d\u5fc5\u4e3a\u4e86\u4f7f\u7528 in \u6216 out \u800c\u523b\u610f\u8bbe\u8ba1\u590d\u6742\u7684\u63a5\u53e3\u3002\u66f4\u597d\u7684\u601d\u8def\u662f\u5148\u660e\u786e\u63a5\u53e3\u7684\u804c\u8d23，\u518d\u51b3\u5b9a\u662f\u5426\u9700\u8981\u53d8\u4f53\u3002<\/p>\n

          \n
        • \u63a5\u53e3\u53ea\u8d1f\u8d23\u63d0\u4f9b\u7ed3\u679c： \u7c7b\u578b\u53c2\u6570\u53ea\u51fa\u73b0\u5728\u8f93\u51fa\u4f4d\u7f6e\u65f6，\u53ef\u4ee5\u8003\u8651\u4f7f\u7528 out，\u8ba9\u6d3e\u751f\u7c7b\u578b\u7684\u63d0\u4f9b\u8005\u80fd\u591f\u7528\u4e8e\u66f4\u901a\u7528\u7684\u63a5\u53e3\u53d8\u91cf\u3002<\/li>\n
        • \u63a5\u53e3\u53ea\u8d1f\u8d23\u63a5\u6536\u6216\u5904\u7406\u5bf9\u8c61： \u7c7b\u578b\u53c2\u6570\u53ea\u51fa\u73b0\u5728\u8f93\u5165\u4f4d\u7f6e\u65f6，\u53ef\u4ee5\u8003\u8651\u4f7f\u7528 in，\u8ba9\u901a\u7528\u5904\u7406\u5668\u4e5f\u80fd\u5904\u7406\u6d3e\u751f\u7c7b\u578b\u3002<\/li>\n
        • \u63a5\u53e3\u65e2\u8bfb\u53d6\u53c8\u5199\u5165\u540c\u4e00\u7c7b\u578b： \u901a\u5e38\u4fdd\u6301\u4e0d\u53d8，\u4f8b\u5982\u5e38\u89c1\u7684\u53ef\u8bfb\u5199\u96c6\u5408\u6216\u4ed3\u50a8\u63a5\u53e3\u3002<\/li>\n
        • \u4f7f\u7528\u6846\u67b6\u63d0\u4f9b\u7684\u63a5\u53e3\u548c\u59d4\u6258： \u4f18\u5148\u4e86\u89e3\u5b83\u4eec\u5df2\u6709\u7684\u89c4\u5219，\u4f8b\u5982 IEnumerable<T>\u3001Action<T> \u548c Func<T, TResult>，\u901a\u5e38\u5c31\u80fd\u89e3\u51b3\u5927\u90e8\u5206\u5b9e\u9645\u95ee\u9898\u3002<\/li>\n<\/ul>\n

          \u5199\u5728\u6700\u540e<\/h4>\n

          \u9006\u53d8\u4e0e\u534f\u53d8\u770b\u8d77\u6765\u62bd\u8c61，\u771f\u6b63\u7406\u89e3\u65f6\u53ea\u9700\u8981\u6293\u4f4f\u4e00\u6761\u4e3b\u7ebf：\u534f\u53d8\u89e3\u51b3\u201c\u7ed3\u679c\u80fd\u4e0d\u80fd\u66f4\u5177\u4f53\u201d，\u9006\u53d8\u89e3\u51b3\u201c\u8f93\u5165\u80fd\u4e0d\u80fd\u66f4\u901a\u7528\u201d\u3002 out \u5e38\u89c1\u4e8e\u63d0\u4f9b\u6570\u636e\u7684\u63a5\u53e3，in \u5e38\u89c1\u4e8e\u63a5\u6536\u6570\u636e\u7684\u63a5\u53e3，\u800c Action\u3001Func \u5219\u628a\u8fd9\u4e9b\u89c4\u5219\u5e26\u8fdb\u4e86\u65e5\u5e38\u59d4\u6258\u4f7f\u7528\u4e2d\u3002<\/p>\n

          \u5f53\u4f60\u518d\u6b21\u9047\u5230 IEnumerable<Dog> \u4e3a\u4ec0\u4e48\u80fd\u8d4b\u503c\u7ed9 IEnumerable<Animal>，\u6216\u8005 Action<Animal> \u4e3a\u4ec0\u4e48\u80fd\u8d4b\u503c\u7ed9 Action<Dog> \u65f6，\u5c31\u53ef\u4ee5\u4ece\u201c\u8f93\u5165\u8fd8\u662f\u8f93\u51fa\u201d\u201c\u7c7b\u578b\u8f6c\u6362\u662f\u5426\u5b89\u5168\u201d\u4e24\u4e2a\u89d2\u5ea6\u5224\u65ad，\u800c\u4e0d\u5fc5\u6b7b\u8bb0\u786c\u80cc\u3002<\/p>\n

          \n

          \u89c9\u5f97\u6709\u6536\u83b7？\u6b22\u8fce\u70b9\u8d5e\u3001\u6536\u85cf\u3002\u7406\u89e3\u6cdb\u578b\u7684\u7c7b\u578b\u8f6c\u6362\u89c4\u5219，\u80fd\u8ba9\u4f60\u5728\u8bbe\u8ba1\u63a5\u53e3\u3001\u4f7f\u7528\u59d4\u6258\u548c\u9605\u8bfb .NET \u6e90\u7801\u65f6\u66f4\u52a0\u5f97\u5fc3\u5e94\u624b\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"

          \u4e00\u53e5\u8bdd\u6982\u62ec： \u534f\u53d8（out）\u8ba9\u201c\u66f4\u5177\u4f53\u7684\u7ed3\u679c\u201d\u53ef\u4ee5\u5f53\u6210\u201c\u66f4\u901a\u7528\u7684\u7ed3\u679c\u201d\u6765\u7528；\u9006\u53d8（in）\u8ba9\u201c\u80fd\u5904\u7406\u66f4\u901a\u7528\u6570\u636e\u7684\u65b9\u6cd5\u201d\u4e5f\u80fd\u5904\u7406\u66f4\u5177\u4f53\u7684\u6570\u636e\u3002\u7406\u89e3\u5b83\u4eec，\u5c31\u80fd\u770b\u61c2 IEnumerable\u3001Action\u3001Func \u80cc\u540e\u7684\u7c7b\u578b\u8f6c\u6362\u89c4\u5219\u3002\u6587\u7ae0\u76ee\u5f55
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