{"id":346,"date":"2024-06-05T23:38:38","date_gmt":"2024-06-05T15:38:38","guid":{"rendered":"https:\/\/cococat.top\/?p=346"},"modified":"2024-06-05T23:38:38","modified_gmt":"2024-06-05T15:38:38","slug":"trait-object-2-implement","status":"publish","type":"post","link":"https:\/\/cococat.top\/index.php\/2024\/06\/05\/trait-object-2-implement\/","title":{"rendered":"\u6df1\u5165\u7406\u89e3\u7279\u5f81\u5bf9\u8c61\u4e4b\u4e8c\uff1a\u4e3a `dyn Trait` \u5b9e\u73b0 `Trait` \u7684\u539f\u7406"},"content":{"rendered":"

\u672c\u6587\u662f rust \u793e\u533a\u5927\u795e quinedot \u7684\u7cfb\u5217\u6587\u7ae0<\/a> \u7684\u7ffb\u8bd1\u7248\u3002\u6211\u5728\u56fd\u5185\u5404\u4e2a\u5e73\u53f0\u4f3c\u4e4e\u90fd\u6ca1\u6709\u770b\u5230\u73b0\u5b58\u7684\u7ffb\u8bd1\uff0c\u56e0\u6b64\u5c1d\u8bd5\u505a\u4e9b\u642c\u8fd0\u5de5\u4f5c\u3002\u7531\u4e8e\u672c\u4eba\u7684\u6280\u672f\u548c\u7ffb\u8bd1\u6c34\u5e73\u90fd\u975e\u5e38\u6709\u9650\uff0c\u96be\u514d\u6709\u9519\u8bef\uff0c\u975e\u5e38\u6b22\u8fce\u5927\u5bb6\u5bf9\u4e0d\u5f53\u4e4b\u5904\u8fdb\u884c\u6307\u6b63\u3002<\/p>\n

\u8fd9\u662f\u672c\u7cfb\u5217\u6587\u7ae0\u7684\u7b2c 2 \u7bc7\u3002<\/p>\n

1. \u524d\u8a00<\/h2>\n

dyn Trait<\/code> \u4f5c\u4e3a\u6240\u6709\u5b9e\u73b0\u4e86 Trait<\/code> \u7684 base type \u7684\u62bd\u8c61\uff0c\u5176\u81ea\u8eab\u5f53\u7136\u4e5f\u9700\u8981\u5b9e\u73b0 Trait<\/code>\u3002\u7f16\u8bd1\u5668\u603b\u662f\u81ea\u52a8\u751f\u6210\u4e86\u8fd9\u4e2a\u5b9e\u73b0\u3002\u6211\u4eec\u63a5\u4e0b\u6765\u8981\u63a2\u8ba8\u8fd9\u79cd\u5b9e\u73b0\u7684\u5de5\u4f5c\u539f\u7406\uff0c\u4ee5\u53ca\u5e26\u6765\u7684\u4e00\u4e9b\u9650\u5236\u3002<\/p>\n

\u6b64\u5916\uff0c\u6211\u4eec\u8fd8\u4f1a\u8bb2\u5230\u4e00\u4e9b\u8ba9\u4eba\u5403\u60ca\u7684 edge case\uff0c\u5176\u4e2d\u4e5f\u6709\u4e00\u90e8\u5206\u4e0e dyn Trait<\/code> \u5b9e\u73b0 Trait<\/code> \u7684\u65b9\u5f0f\u76f8\u5173\u3002<\/p>\n

2. dyn Trait<\/code> \u5982\u4f55\u5b9e\u73b0 Trait<\/code><\/h2>\n

\u9996\u5148\u9700\u8981\u58f0\u660e\u7684\u662f\uff0c\u4e0b\u9762\u7684\u4ee3\u7801\u662f\u4e3a dyn Trait<\/code> \u5b9e\u73b0\u7279\u5f81 Trait<\/code> \u7684\u4e00\u79cd\u53ef\u80fd\u7684\u5b9e\u73b0<\/strong>\uff0c\u8fd9\u53ea\u662f\u4e00\u4efd\u7c97\u7565\u7684\u6982\u8ff0\uff0c\u800c\u975e\u771f\u5b9e rust \u7f16\u8bd1\u5668\u4e2d\u7684\u5199\u6cd5\u3002rust \u7f16\u8bd1\u5668\u7684\u5b9e\u9645\u5904\u7406\u903b\u8f91\u5305\u542b\u4e86\u5f88\u591a\u7ec6\u8282\uff0c\u800c\u90a3\u4e9b\u90fd\u662f\u4ee3\u7801\u5b9e\u73b0\u65b9\u9762\u7684\u4e8b\u60c5\u3002\u672c\u6587\u7684\u51fa\u53d1\u70b9\u662f\uff0c\u901a\u8fc7\u5c55\u793a\u4e00\u79cd\u7b80\u660e\u7684\u53ef\u80fd\u5b9e\u73b0\u65b9\u5f0f\uff0c\u8ba9\u8bfb\u8005\u5bf9\u7279\u5f81\u5bf9\u8c61\u4f5c\u4e3a\u4e00\u4e2a\u5177\u4f53\u7c7b\u578b\u6709\u76f4\u89c2\u7684\u7406\u89e3\uff0c\u5e76\u4e14\u8ba4\u8bc6\u5230\u7279\u5f81\u5bf9\u8c61\u5b58\u5728\u4e00\u4e9b\u4f7f\u7528\u9650\u5236\u7684\u539f\u56e0\u3002<\/p>\n

\u58f0\u660e\u8fc7\u540e\uff0c\u6211\u4eec\u5148\u7ed9\u51fa\u4e00\u4e2a Trait<\/code> \u7684\u5b9a\u4e49\uff1a<\/p>\n

trait Trait {\n    fn look(&self);\n    fn add(&mut self, s: String) -> i32;\n}<\/code><\/pre>\n
\u63a5\u4e0b\u6765\u6211\u4eec\u6765\u770b\u770b\u7f16\u8bd1\u5668\u5bf9\u8fd9\u4e2a\u7279\u5f81\u7684\u5b9e\u73b0\u53ef\u80fd\u4f1a\u662f\u4ec0\u4e48\u6837\u5b50\u3002\u56de\u5fc6\u4e00\u4e0b\u524d\u4e00\u7bc7\u6587\u7ae0\u7684\u5185\u5bb9\uff0c\u5f53\u6784\u5efa\u7279\u5f81\u5bf9\u8c61\u65f6\uff0c\u6211\u4eec\u9700\u8981\u4e00\u4e2a\u6307\u5411\u64e6\u9664\u7684 base type \u7684\u6307\u9488\uff0c\u4ee5\u53ca\u4e00\u4e2a\u865a\u8868\u3002\u56e0\u6b64\uff0c\u4e00\u79cd\u53ef\u80fd\u7684 &dyn Trait<\/code> \u7ed3\u6784\u662f\u8fd9\u6837\u7684\uff1a<\/p>\n
#[repr(C)]\nstruct DynTraitRef<'a> {\n    _lifetime: PhantomData<&'a ()>,\n    base_type: *const (),\n    vtable: &'static DynTraitVtable,\n}\n\n\/\/ \u4f2a\u7801\ntype &'a dyn Trait = DynTraitRef<'a>;<\/code><\/pre>\n
\u8fd9\u91cc\u6211\u4eec\u4f7f\u7528\u4e86\u4e00\u4e2a\u7a84\u6307\u9488 *const ()<\/code> \u6765\u6307\u5411\u64e6\u9664\u7684 base type\u3002\u7c7b\u4f3c\u5730\uff0c\u5bf9\u4e8e &'a mut dyn Trait<\/code>\uff0c\u6211\u4eec\u53ef\u4ee5\u7565\u52a0\u6539\u52a8\u5b9e\u73b0\u4e00\u4e2a DynTraitMut<'a><\/code> \u7ed3\u6784\uff0c\u800c\u5b83\u7684 base type \u6307\u9488\u5e94\u5f53\u6362\u6210 *mut ()<\/code>\u3002<\/p>\n
\u5bf9\u4e8e\u4e0a\u9762\u4ee3\u7801\u4e2d\u7684\u865a\u8868 DynTraitVtable<\/code>\uff0c\u4e00\u79cd\u53ef\u80fd\u7684\u7ed3\u6784\u662f\u8fd9\u6837\u7684\uff1a<\/p>\n
#[repr(C)]\nstruct DynTraitVtable {\n    fn_drop: fn(*mut ()),\n    type_size: usize,\n    type_alignment: usize,\n    fn_look: fn(*const ()),\n    fn_add: fn(*mut (), s: String) -> i32,\n}<\/code><\/pre>\n
\u5728\u5b8c\u6210\u4e86\u6240\u6709 struct \u7684\u58f0\u660e\u540e\uff0c\u73b0\u5728\u8be5\u4e3a dyn Trait<\/code> \u5b9e\u73b0 Trait<\/code> \u4e86\uff0c\u4e00\u79cd\u53ef\u80fd\u7684\u5199\u6cd5\u662f\uff1a<\/p>\n
impl Trait for dyn Trait + '_ {\n    fn look(&self) {\n        (self.vtable.fn_look)(self.base_type)\n    }\n    fn add(&mut self, s: String) -> i32 {\n        (self.vtable.fn_add)(self.base_type, s)\n    }\n}<\/code><\/pre>\n
\u603b\u7ed3\u4e00\u4e0b\uff0c\u6211\u4eec\u5c06\u6307\u5411 base type \u7684\u5f15\u7528\u66ff\u6362\u4e3a\u4e86\u6307\u5411\u540c\u4e00\u5757\u6570\u636e\u7684\u5408\u9002\u7c7b\u578b<\/strong>\u7684\u6307\u9488\uff0c\u4ece\u800c\u64e6\u9664\u4e86\u539f\u59cb\u7684\u7c7b\u578b\u3002\u65e0\u8bba\u662f\u5728\u5bbd\u5f15\u7528\uff08&dyn Trait<\/code>\u3001&mut dyn Trait<\/code>\uff09\u4e2d\uff0c\u8fd8\u662f\u5728\u865a\u8868\u7684\u51fd\u6570\u6307\u9488\u4e2d\uff0c\u90fd\u662f\u91c7\u7528\u8fd9\u79cd\u65b9\u6cd5\u3002\u5728\u8fd9\u8fc7\u7a0b\u4e2d\u7f16\u8bd1\u5668\u4fdd\u8bc1\u4e0d\u51fa\u73b0 ABI \u4e0d\u5339\u914d\uff08ABI mismatch\uff09\u3002<\/p>\n
\n
\u8bd1\u6ce8\uff1a\u8fd9\u91cc\u201c\u5408\u9002\u7c7b\u578b\u7684\u6307\u9488\u201d\u7684\u610f\u601d\u662f\uff0c\u65e0\u8bba\u662f\u6307\u5411\u4ee3\u7801\u6bb5\u91cc\u7684\u51fd\u6570\uff0c\u8fd8\u662f\u6307\u5411\u5806\u4e0a\u7684\u6570\u636e\uff0c\u9700\u8981\u6839\u636e\u60c5\u51b5\u4e3a\u6307\u9488\u9009\u62e9\u6b63\u786e\u7684\u7c7b\u578b\u3002\u4f8b\u5982\u865a\u8868\u4e2d\u6307\u5411 look()<\/code> \u65b9\u6cd5\u7684\u51fd\u6570\u6307\u9488\uff0c\u5c31\u9700\u8981\u7b26\u5408 look()<\/code> \u672c\u8eab\u7684\u51fd\u6570\u7b7e\u540d\uff1b\u800c\u5728 DynTraitRef<\/code> \u91cc\u6307\u5411\u53d8\u91cf\u672c\u8eab\u7684 base_type<\/code> \u6307\u9488\uff0c\u5c31\u9700\u8981\u662f *const ()<\/code> \u7c7b\u578b\u3002<\/p>\n<\/blockquote>\n
\u8fd9\u91cc\u518d\u6b21\u5f3a\u8c03\u4e0b\uff1a\u4e0a\u8ff0\u4ee3\u7801\u53ea\u662f\u4e00\u79cd\u53ef\u80fd\u7684\u5b9e\u73b0\u65b9\u5f0f\uff0c\u76ee\u7684\u5728\u4e8e\u5e2e\u52a9\u7406\u89e3\u548c\u8fdb\u884c\u63a2\u8ba8\uff0c\u800c\u975e\u7f16\u8bd1\u5668\u4e2d\u7684\u786e\u5207\u5b9e\u73b0\u3002<\/p>\n
\u5173\u4e8e\u8fd9\u4e2a\u8bdd\u9898\u8fd8\u6709\u53e6\u4e00\u7bc7\u535a\u5ba2\u6587\u7ae0<\/a>\u53ef\u4ee5\u4e00\u8bfb\u3002\u4e0d\u8fc7\u8bf7\u6ce8\u610f\uff0c\u5b83\u5199\u4e8e 2015 \u5e74\uff0c\u81ea\u90a3\u65f6\u4ee5\u6765 Rust \u5728\u8bb8\u591a\u65b9\u9762\u90fd\u53d1\u751f\u4e86\u53d8\u5316\u3002\u4f8b\u5982\uff0c\u7279\u5f81\u5bf9\u8c61\u8fc7\u53bb\u7684\u8bed\u6cd5\u4ec5\u4ec5\u662f Trait<\/code> \u800c\u4e0d\u662f dyn Trait<\/code><\/a>\u3002\u56e0\u6b64\uff0c\u4f60\u5fc5\u987b\u6839\u636e\u4e0a\u4e0b\u6587\u5224\u65ad\u4f5c\u8005\u662f\u5728\u8ba8\u8bba\u7279\u5f81\u8fd8\u662f\u7279\u5f81\u5bf9\u8c61\u7c7b\u578b\u3002<\/p>\n
3. \u5b9e\u73b0\u5176\u4ed6 receiver \u7c7b\u578b\u7684\u65b9\u6cd5<\/h2>\n
\u8ba9\u6211\u4eec\u770b\u4e00\u4e0b\u53e6\u4e00\u4e2a\u65b9\u6cd5\uff0c\u5176\u51fd\u6570\u7b7e\u540d\u7684 receiver \u7684\u7c7b\u578b\u4e0d\u662f\u5bf9\u81ea\u8eab\u7684\u5f15\u7528\uff0c\u800c\u662f Box<\/code> :<\/p>\n
trait Trait {\n    fn eat_box(self: Box<Self>);\n}<\/code><\/pre>\n
\u5982\u679c\u6211\u4eec\u8981\u4e3a\u7279\u5f81\u5bf9\u8c61\u5b9e\u73b0 Trait<\/code>\uff0c\u90a3\u4e48\u5bf9\u4e8e\u65b9\u6cd5 eat_box<\/code>\uff0c\u5176 self<\/code> \u7684\u7c7b\u578b\u5c31\u5e94\u5f53\u662f Box<dyn Trait><\/code> \u4e86\uff0c\u8fd9\u65f6\u6211\u4eec\u5e94\u8be5\u600e\u4e48\u505a\u5462\uff1f\u4ece\u5185\u5b58\u7ed3\u6784\u6765\u770b\uff0cBox<BaseType \/* : Sized *\/><\/code> \u662f\u4e00\u4e2a\u7a84\u6307\u9488\uff0c\u800c Box<dyn Trait><\/code> \u662f\u4e00\u4e2a\u5bbd\u6307\u9488\uff0c\u975e\u5e38\u7c7b\u4f3c\u4e8e &mut dyn Trait<\/code>\uff08\u5c3d\u7ba1\u4e5f\u6709\u4e00\u4e9b\u4e0d\u540c\uff1a Box<\/code> \u62e5\u6709\u5176\u6307\u5411\u5bf9\u8c61\u7684\u6240\u6709\u6743\uff0c\u800c\u53ef\u53d8\u5f15\u7528 &mut<\/code> \u5e76\u975e\u5982\u6b64\uff09\u3002\u56e0\u6b64\u8fd9\u91cc\u6574\u4f53\u7684\u601d\u8def\u4e5f\u662f\u7c7b\u4f3c\u4e8e &mut dyn Trait<\/code> \u7684:<\/p>\n
\/\/ \u4e0b\u9762\u7684\u4ee3\u7801\u4ecd\u7136\u53ea\u662f\u4e3a\u4e86\u6f14\u793a\u76ee\u7684\nimpl Trait for dyn Trait + '_ {\n    fn eat_box(self: Box<Self>) {\n        let BoxRepresentation { base_type, vtable } = self;\n        let boxed_type = Box::from_raw(base_type);\n        (vtable.fn_eat_box)(boxed_type);\n    }\n}<\/code><\/pre>\n
\u7b80\u800c\u8a00\u4e4b\uff0c\u5bf9\u4e8e\u4e00\u4e9b\u53d7\u652f\u6301\u7684 receiver \u7c7b\u578b\uff0c\u4f8b\u5982 &self<\/code>\u3001Box<Self><\/code> \u7b49\uff0c\u7f16\u8bd1\u5668\u80fd\u591f\u81ea\u52a8\u5730\u5c06\u5b83\u4eec\u4ece\u7c7b\u578b\u64e6\u9664\u7684\u5f62\u5f0f\uff08\u5982 Box<Self><\/code>\uff0c\u8fd9\u91cc Self<\/code> \u662f\u7279\u5f81\u5bf9\u8c61\uff09\u8f6c\u6362\u6210\u5bf9 base type\uff08Box<BaseType><\/code>\uff09ABI \u517c\u5bb9\u7684\u5f62\u5f0f\u3002\u73b0\u9636\u6bb5\uff0c\u8fd9\u4e2a\u8f6c\u6362\u64cd\u4f5c\u4e0e\u7279\u5f81 DispatchFromDyn<\/code><\/a> \u6709\u5173\u3002\u76ee\u524d\u6240\u6709\u53d7\u652f\u6301\u7684\u7c7b\u578b\u90fd\u5728\u8fd9\u4e2a\u7279\u5f81\u7684\u6587\u6863\u4e2d\u5217\u51fa\u4e86\uff0c\u6ce8\u610f\u5176\u4e2d\u6709\u4e9b\u7c7b\u578b\u662f\u53ea\u5728 unstable \u7684 arbitrary_self_types<\/code> feature \u4e0b\u53d7\u652f\u6301\u7684\u3002<\/p>\n
4. Supertrait \u7684\u5b9e\u73b0<\/h2>\n
\u6211\u4eec\u7a0d\u540e\u4f1a\u66f4\u8be6\u7ec6\u5730\u770b\u4e00\u4e0b supertraits\uff08TODO:\uff09\uff0c\u4f46\u5728\u8fd9\u91cc\u6211\u4eec\u5148\u7ed9\u51fa\u4e00\u4e2a\u7b80\u5355\u7684\u7ed3\u8bba\uff1a\u5f53\u4f60\u6709\u4e00\u4e2a supertrait \u65f6\uff1a<\/p>\n
trait SuperTrait { \/* ... *\/ }\ntrait Trait: SuperTrait { \/* ... *\/ }<\/code><\/pre>\n
\u90a3\u4e48\u7f16\u8bd1\u5668\u4e5f\u4f1a\u81ea\u52a8\u4e3a dyn Trait<\/code> \u5b9e\u73b0 SuperTrait<\/code> \uff0c\u6b63\u5982\u4ed6\u4f1a\u81ea\u52a8\u5b9e\u73b0 Trait<\/code> \u4e00\u6837\u3002\u6b64\u65f6\u7684\u865a\u8868\u4e2d\u4f1a\u5305\u542b SuperTrait<\/code> \u7684\u65b9\u6cd5\u3002<\/p>\n
5. Box<dyn Trait><\/code> \u548c &dyn Trait<\/code> \u5e76\u4e0d\u81ea\u52a8\u5b9e\u73b0 Trait<\/code><\/h2>\n
\u4e8b\u5b9e\u4e0a\uff0cBox<dyn Trait><\/code> \u548c &dyn Trait<\/code> \u5e76\u4e0d\u4f1a\u81ea\u52a8\u5b9e\u73b0 Trait<\/code>\uff0c\u8fd9\u53ef\u80fd\u4f1a\u8ba9\u4eba\u5f88\u60ca\u8bb6\u3002\u4e3a\u4ec0\u4e48\u5462\uff1f\u539f\u56e0\u5f88\u7b80\u5355\uff1a\u8fd9\u5e76\u4e0d\u603b\u662f\u53ef\u80fd\u7684\u3002<\/p>\n
\u6b63\u5982\u6211\u4eec\u7a0d\u540e\u4f1a\u8bb2\u5230\u7684\uff08TODO:\uff09\uff0c\u4e00\u4e2a\u7279\u5f81\u53ef\u80fd\u542b\u6709\u65e0\u6cd5\u901a\u8fc7 dyn Trait<\/code> \u5206\u53d1\u7684\u65b9\u6cd5\uff0c\u4f46\u8fd9\u4e9b\u65b9\u6cd5\u53c8\u5fc5\u987b\u4e3a\u6240\u6709\u7684\u5b9a\u957f\u7c7b\u578b\uff08Sized<\/code>\uff09\u5b9e\u73b0\u3002\u4e00\u4e2a\u5178\u578b\u7684\u4f8b\u5b50\u662f\u6ca1\u6709 receiver \u7684\u5173\u8054\u51fd\u6570\uff1a<\/p>\n
trait Trait {\n    fn no_receiver() -> String where Self: Sized;\n}<\/code><\/pre>\n
\u5bf9\u4e8e\u8fd9\u6837\u7684\u5173\u8054\u51fd\u6570\uff0c\u7f16\u8bd1\u5668\u6ca1\u6709\u529e\u6cd5\u751f\u6210\u51fd\u6570\u4f53\uff0c\u65e0\u6cd5\u5b9e\u73b0\u8fd9\u4e2a\u8fd9\u4e2a\u65b9\u6cd5\uff0c\u8fdb\u800c\u5bfc\u81f4\u4e0d\u80fd\u5b9e\u73b0 Trait<\/code> \u3002<\/p>\n
\u53e6\u5916\uff0c\u5206\u53d1\u65b9\u6cd5\u7684 receiver \u5e76\u4e0d\u603b\u662f\u6709\u610f\u4e49\u7684\uff1a<\/p>\n
trait Trait {\n    fn takes_mut(&mut self);\n}<\/code><\/pre>\n
\u5bf9\u4e8e &dyn Trait<\/code> \uff0c\u7f16\u8bd1\u5668\u53ef\u4ee5\u4ece\u5bbd\u6307\u9488\u4e2d\u83b7\u53d6 &BaseType<\/code>\uff0c\u4f46\u65e0\u6cd5\u83b7\u53d6\u5230 &mut BaseType<\/code>\uff0c\u6240\u4ee5\u7f16\u8bd1\u5668\u65e0\u6cd5\u4e3a &dyn Trait<\/code> \u5b9e\u73b0 Trait::takes_mut()<\/code>\u3002<\/p>\n
\u540c\u6837\u5730\uff0c\u4e00\u4e2a Arc<dyn Trait><\/code> \u6ca1\u6709\u529e\u6cd5\u8c03\u7528 Box<dyn Trait><\/code>\uff08\u8bd1\u6ce8\uff1aArc<dyn Triat><\/code> \u5e76\u4e0d\u62e5\u6709\u5bf9\u8c61\u7684\u6240\u6709\u6743\uff09\uff0c\u53cd\u4e4b\u4ea6\u7136\uff0c\u7b49\u7b49\u3002\u2018<\/p>\n
5.1. \u53ef\u4ee5\u624b\u52a8\u5b9e\u73b0<\/h3>\n
\u5982\u679c Trait<\/code> \u662f\u4e00\u4e2a\u672c\u5730\u7279\u5f81\uff08local trait\uff09\uff0c\u90a3\u4e48\u6211\u4eec\u53ef\u4ee5\u4e3a Box<dyn Trait + '_><\/code> \u7b49\u5b9e\u73b0\u5b83\uff0c\u5c31\u548c\u5176\u4ed6\u7c7b\u578b\u4e00\u6837\u3002\u4e0d\u8fc7\u8981\u5c0f\u5fc3\uff0c\u5f88\u5bb9\u6613\u8bef\u5199\u6210\u9012\u5f52\u5b9a\u4e49\uff01\u6211\u4eec\u7a0d\u540e\uff08TODO:\uff09\u4f1a\u901a\u8fc7\u4e00\u4e2a\u4f8b\u5b50\u6765\u8bb2\u89e3\u8fd9\u4e00\u70b9\u3002<\/p>\n
\u6b64\u5916\uff0c&T<\/code>\u3001&mut T<\/code> \u548c Box<T><\/code> \u662f\u57fa\u7840\u7c7b\u578b\uff08fundamental type<\/a>\uff09\uff0c\u8fd9\u4f7f\u5f97\u5728\u5b64\u513f\u89c4\u5219\uff08\u51b3\u5b9a\u4f60\u53ef\u4ee5\u624b\u52a8\u5b9e\u73b0\u54ea\u4e9b\u7279\u5f81\uff09\u65b9\u9762\uff0c\u5b83\u4eec\u7684\u884c\u4e3a\u4e0e T<\/code> \u76f8\u540c\u3002\u53e6\u5916\uff0c\u5982\u679c Trait<\/code> \u662f\u4e00\u4e2a\u672c\u5730\u7279\u5f81\uff08local trait\uff09\uff0c\u5219 dyn Trait + '_<\/code> \u662f\u4e00\u4e2a\u672c\u5730\u7c7b\u578b\uff08local type\uff09\u3002<\/p>\n
\u4e0a\u8ff0\u6027\u8d28\u52a0\u5728\u4e00\u8d77\uff0c\u610f\u5473\u7740\u6211\u4eec\u53ef\u4ee5\u4e3a Box<dyn Trait + '_><\/code>\uff08\u548c\u5176\u4ed6\u542b\u6709\u57fa\u7840\u7c7b\u578b\u7684 wrapper\uff09\u624b\u52a8\u5b9e\u73b0\u5176\u4ed6<\/strong>\u7279\u5f81\uff0c\u5305\u62ec\u4f46\u4e0d\u9650\u4e8e Trait<\/code>\u3002<\/p>\n
\u6211\u4eec\u7a0d\u540e\u4e5f\u4f1a\u6709\u8fd9\u65b9\u9762\u7684\u4f8b\u5b50\uff08TODO:\uff09\u3002<\/p>\n
\u4e0d\u5e78\u7684\u662f\uff0cRc<\/code>\u3001Arc<\/code> \u7b49\u5e76\u4e0d\u662f\u57fa\u7840\u7c7b\u578b\uff0c\u56e0\u6b64\u5e76\u975e\u6240\u6709\u573a\u666f\u90fd\u80fd\u8fd9\u4e48\u5e72\u3002<\/p>\n
\n
\u8bd1\u6ce8\uff1a\u8fd9\u91cc\u989d\u5916\u89e3\u91ca\u4e00\u4e0b\u51e0\u4e2a\u540d\u8bcd\uff1a<\/p>\n