{"id":348,"date":"2024-06-22T16:47:55","date_gmt":"2024-06-22T08:47:55","guid":{"rendered":"https:\/\/cococat.top\/?p=348"},"modified":"2024-06-22T16:47:55","modified_gmt":"2024-06-22T08:47:55","slug":"trait-object-3-coercion","status":"publish","type":"post","link":"https:\/\/cococat.top\/index.php\/2024\/06\/22\/trait-object-3-coercion\/","title":{"rendered":"\u6df1\u5165\u7406\u89e3\u7279\u5f81\u5bf9\u8c61\u4e4b\u4e09\uff1a\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362"},"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 3 \u7bc7\u3002<\/p>\n

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

\u5728 rust \u4e2d\uff0c\u6211\u4eec\u901a\u5e38\u4f7f\u7528\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\uff08coercion\uff09\u6765\u5c06\u4e00\u4e9b\u7c7b\u578b\u8f6c\u6362\u4e3a\u7279\u5f81\u5bf9\u8c61\uff0c\u4e0b\u9762\u662f\u7528\u51fd\u6570\u5f62\u5f0f\u5199\u51fa\u7684\u4e00\u4e9b\u5178\u578b\u573a\u666f\uff1a<\/p>\n

fn coerce_ref<'a, T: Trait + Sized + 'a>(t:    &T ) -> &(  dyn Trait + 'a) { t }\nfn coerce_box<'a, T: Trait + Sized + 'a>(t: Box<T>) -> Box<dyn Trait + 'a> { t }\nfn coerce_arc<'a, T: Trait + Sized + 'a>(t: Arc<T>) -> Arc<dyn Trait + 'a> { t }<\/code><\/pre>\n
\u5728\u5b9e\u8df5\u4e2d\uff0c\u6211\u4eec\u770b\u5230\u7684\u4ee3\u7801\u5f80\u5f80\u4e0d\u4f1a\u8fd9\u6837\u7e41\u6742\uff0c\u56e0\u4e3a\u8fd9\u91cc\u5f15\u5165\u4e86\u4e00\u4e9b\u663e\u5f0f\u751f\u547d\u5468\u671f\u548c\u7279\u5f81\u7ea6\u675f\uff0c\u800c\u901a\u5e38\u8fd9\u4e9b\u7ea6\u675f\u90fd\u662f\u9690\u542b\u7684\u6216\u8005\u65e0\u9700\u4f7f\u7528\u3002\u4f8b\u5982\uff0c\u6cdb\u578b\u7c7b\u578b\u53c2\u6570\u4e0a\u7684 Sized<\/code> \u7ea6\u675f\u4e00\u822c\u662f\u9690\u542b\u7684\uff0c\u4f46\u4e0a\u9762\u7684\u4ee3\u7801\u91cc\u6211\u4eec\u663e\u5f0f\u5730\u6807\u51fa\uff0c\u5f3a\u8c03\u6b63\u5728\u8ba8\u8bba\u7684 base type \u90fd\u662f\u5b9a\u957f\u7c7b\u578b\uff08Sized<\/code>\uff09\u3002<\/p>\n
\u5047\u8bbe\u7279\u5f81 Trait<\/code> \u662f\u5bf9\u8c61\u5b89\u5168\uff08object safe\uff09\u7684\uff0c\u5e76\u4e14\u6ee1\u8db3 T: 'a + Trait + Sized<\/code>\uff0c\u90a3\u4e48\u5bf9\u4e8e\u4e00\u4e9b\u53d7\u652f\u6301\u7684\u6307\u9488\u7c7b\u578b Ptr<\/code>\uff08\u5982 &_<\/code> \u548c Box<_><\/code>\uff09\uff0c\u6211\u4eec\u5c31\u53ef\u4ee5\u5c06 Ptr<T><\/code> \u5f3a\u5236\u8f6c\u6362\u6210 Ptr<dyn Trait + 'a><\/code>\u3002<\/p>\n
\u5982\u679c\u6211\u4eec\u60f3\u8981\u4e00\u4e2a dyn Trait + Send + 'a<\/code>\uff0c\u81ea\u7136\u6211\u4eec\u4e5f\u9700\u8981 T: Send<\/code>\uff0c\u5bf9\u4e8e\u4efb\u4f55\u5176\u4ed6\u81ea\u52a8\u7279\u5f81\uff08auto trait\uff09\u4e5f\u662f\u5982\u6b64\u3002<\/p>\n
\u5728\u672c\u6587\u7684\u5176\u4f59\u90e8\u5206\uff0c\u6211\u4eec\u5c06\u7814\u7a76\u8fd9\u4e9b\u5178\u578b\u6848\u4f8b\u4e4b\u5916\u7684\u60c5\u51b5\uff0c\u4ee5\u53ca\u5f3a\u5236\u8f6c\u6362\u7684\u4e00\u4e9b\u4f7f\u7528\u9650\u5236\u3002<\/p>\n
2. \u5173\u8054\u7c7b\u578b\uff08associate type\uff09<\/h2>\n
\u5f53\u4e00\u4e2a\u7279\u5f81\u62e5\u6709\u4e00\u6216\u591a\u4e2a\u975e\u6cdb\u578b\u7684\u5173\u8054\u7c7b\u578b\u65f6\uff0c\u8be5\u7279\u5f81\u7684\u6bcf\u4e2a\u5177\u4f53\u5b9e\u73b0\u7c7b\u578b\uff0c\u90fd\u4f1a\u4e3a\u5404\u5173\u8054\u7c7b\u578b\u9009\u62e9\u4e00\u4e2a\u552f\u4e00\u786e\u5b9a\u7684\u3001\u9759\u6001\u53ef\u77e5\u7684\u7c7b\u578b\u3002\u4e5f\u5c31\u662f\u8bf4\uff0c\u6211\u4eec\u53ef\u4ee5\u628a\u5173\u8054\u7c7b\u578b\u7406\u89e3\u6210\u67d0\u4e2a base type \u52a0\u5176\u5b9e\u73b0\u7684\u7279\u5f81\u7684 \u201c\u8f93\u51fa\u201d\u3002<\/p>\n
\u90a3\u4e48\uff0c\u4e3a dyn Trait<\/code> \u5b9e\u73b0 Trait<\/code> \u65f6\uff0c\u5e94\u8be5\u5982\u4f55\u786e\u5b9a\u542b\u6709\u7684\u5173\u8054\u7c7b\u578b\u5462\uff1f\u8fd9\u4e2a\u95ee\u9898\u6ca1\u6709\u552f\u4e00\u786e\u5b9a\u7684\u7b54\u6848\uff0c\u5b9e\u9645\u4e0a\uff0c\u5728\u8fd9\u79cd\u60c5\u51b5\u4e0b\uff0c\u5173\u8054\u7c7b\u578b\u4f1a\u968f\u7740\u88ab\u64e6\u9664\u7684 base type \u53d8\u5316\u3002<\/p>\n
\u8fd9\u6837\u4e00\u6765\uff0c\u77db\u76fe\u5c31\u51fa\u73b0\u4e86\uff1a\u8fd9\u4e0e\u6211\u4eec\u6700\u5f00\u59cb\u63d0\u5230\u7684\u201c\u7279\u5f81\u7684\u5b9e\u73b0\u8005\u5e94\u8be5\u5bf9\u6bcf\u4e2a\u5173\u8054\u7c7b\u578b\u552f\u4e00\u786e\u5b9a\u201d\u7684\u539f\u5219\u662f\u76f8\u8fdd\u80cc\u7684\u3002\u5bf9\u4e8e\u8fd9\u4e2a\u95ee\u9898\uff0c\u4e00\u4e2a\u7b80\u5355\u7c97\u66b4\u7684\u89e3\u51b3\u65b9\u6cd5\u662f\uff1a\u4e00\u65e6\u7279\u5f81 Trait<\/code> \u542b\u6709\u5173\u8054\u7c7b\u578b\uff0c\u90a3\u6211\u4eec\u5c31\u7d22\u6027\u7981\u6b62\u6784\u5efa dyn Trait<\/code> \u7684\u7279\u5f81\u5bf9\u8c61\u3002\u7136\u800c\u5018\u82e5\u771f\u7684\u5f15\u5165\u8fd9\u79cd\u89c4\u5219\uff0c\u5c31\u4f1a\u8ba9\u7279\u5f81\u5bf9\u8c61\u7684\u5b9e\u7528\u6027\u5927\u6253\u6298\u6263\uff0crust \u7684\u8bbe\u8ba1\u8005\u4eec\u65e0\u6cd5\u63a5\u53d7\u8fd9\u79cd\u505a\u6cd5\u3002\u6700\u7ec8\uff0crust \u56e2\u961f\u91c7\u7528\u7684\u65b9\u6848\u662f\uff0c\u8ba9\u7279\u5f81\u4e2d\u7684\u5173\u8054\u7c7b\u578b\u672c\u8d28\u4e0a\u6210\u4e3a dyn Trait<\/code> \u7c7b\u578b\u6784\u9020\u5668\u7684\u5177\u540d\u53c2\u6570\uff08named parameter\uff09\u3002\uff08\u56de\u60f3\u4e00\u4e0b\u672c\u7cfb\u5217\u6587\u7ae0\u7684\u7b2c\u4e00\u7bc7\uff0c\u7531\u4e8e\u7279\u5f81\u5bf9\u8c61\u7684\u751f\u547d\u5468\u671f\uff0cdyn Trait<\/code> \u672c\u8d28\u4e0a\u662f\u4e00\u4e2a\u7c7b\u578b\u6784\u9020\u5668\uff0cdyn Trait + 'a<\/code> \u624d\u662f\u4e00\u4e2a\u5177\u4f53\u7c7b\u578b\uff0c\u53ea\u662f 'a<\/code> \u5f80\u5f80\u88ab\u9690\u85cf\u3002\uff09<\/p>\n
\u4f8b\u5982\uff0c\u5982\u679c\u7ed9\u51fa<\/p>\n
trait Iterator {\n    type Item;\n    fn next(&mut self) -> Option<Self::Item>;\n}<\/code><\/pre>\n
\u90a3\u4e48\u53ef\u4ee5\u6709\uff1a<\/p>\n
dyn Iterator<Item = String> + '_\ndyn Iterator<Item = i32> + '_\ndyn Iterator<Item = f64> + '_<\/code><\/pre>\n
\u7b49\u7b49\u3002\u5728 dyn Trait<...><\/code> \u4e2d\u7684\u5173\u8054\u7c7b\u578b\u5fc5\u987b\u89e3\u6790\u4e3a\u5177\u4f53\u7c7b\u578b\uff0c\u4ee5\u4fbf dyn Trait<...><\/code> \u6210\u4e3a\u4e00\u4e2a\u5177\u4f53\u7c7b\u578b\u3002<\/p>\n
\u5982\u679c\u4f60\u5728 Iterator<\/code> \u7684\u5b9e\u73b0\u4e2d\u6307\u5b9a\u4e86 type Item = String<\/code>\uff0c\u90a3\u4e48\u5f88\u81ea\u7136\u5730\uff0c\u4f60\u5c31\u53ea\u80fd\u5c06\u7c7b\u578b\u5f3a\u5236\u8f6c\u6362\u4e3a dyn Iterator<Item = String><\/code> \u4e86\u3002\u4e0b\u9762\u7684\u5199\u6cd5\u53cd\u6620\u4e86\u5173\u8054\u7c7b\u578b\u7279\u5f81\u7ea6\u675f\u7684\u6837\u5f0f\uff1a<\/p>\n
fn takes_string_iter<Iter>(i: Iter)\nwhere\n    Iter: Iterator<Item = String>,\n{\n   \/\/ ...\n}<\/code><\/pre>\n
\u4f7f\u7528\u5177\u540d\u53c2\u6570\u6709\u8bb8\u591a\u597d\u5904\u3002\u9996\u5148\uff0c\u4e00\u4e2a\u7c7b\u578b\u548c\u5b83\u62e5\u6709\u7684\u5177\u540d\u53c2\u6570\u5f80\u5f80\u5177\u6709\u5f88\u5f3a\u7684\u903b\u8f91\u5173\u8054\uff0c\u4f8b\u5982\u5177\u540d\u53c2\u6570\u80fd\u591f\u6e05\u6670\u5730\u8868\u793a\u4e00\u4e2a Iterator<\/code> \u8fd4\u56de\u7684 Item<\/code> \u662f\u4ec0\u4e48\uff08\u5f53\u7136\uff0c\u8fd9\u4e9b\u5173\u8054\u7c7b\u578b\u9700\u8981\u547d\u540d\u5f97\u5f53\uff09\u3002\u5176\u6b21\uff0c\u5b83\u8fd8\u907f\u514d\u4e86\u5728\u6cdb\u578b\u5217\u8868\u4e2d\u5bf9\u591a\u4e2a\u5173\u8054\u7c7b\u578b\u8fdb\u884c\u6392\u5e8f\uff0c\u4f8b\u5982\u6309\u5b57\u5178\u5e8f\u6392\u5217\u6216\u662f\u6309\u58f0\u660e\u987a\u5e8f\uff0c\u5c24\u5176\u662f\u540e\u8005\uff0c\u5f88\u5bb9\u6613\u51fa\u5dee\u9519\u3002<\/p>\n
\n
\u8bd1\u6ce8\uff1a\u5982\u679c\u4e0d\u662f\u5177\u540d\u53c2\u6570\uff0c\u90a3\u4e48\u53ef\u80fd\u4f1a\u51fa\u73b0\u8fd9\u79cd\u60c5\u51b5\uff1a<\/p>\n
trait Trait {\n    type Assoc1;\n    type Assoc2;\n    type Assoc3;\n}\n\n\/\/ \u5982\u679c\u91c7\u7528\u4e0b\u9762\u8fd9\u79cd\u8bed\u6cd5\uff0c\u4e00\u65e6\u5173\u8054\u7c7b\u578b\u6570\u91cf\u8f83\u591a\uff0c\u8bfb\u8005\u5c31\u5f88\u96be\u7acb\u523b\u5c06 i32<\/code> String<\/code> &[u8]<\/code> \u4e0e Assoc1\/2\/3 \u5bf9\u53f7\u5165\u5ea7\nlet d: Box = ...; \/\/ \u5e76\u975e\u771f\u5b9e\u8bed\u6cd5\n\/\/ \u800c\u5982\u679c\u91c7\u7528\u5177\u540d\u53c2\u6570\u7684\u5199\u6cd5\uff0c\u5c31\u6e05\u6670\u5f97\u591a\uff1a\nlet d: Box = ...;<\/code><\/pre>\n<\/blockquote>\n
\u7136\u800c\uff0c\u8fd9\u4e9b\u5177\u540d\u53c2\u6570\u5fc5\u987b\u5728\u666e\u901a\u6cdb\u578b\u7c7b\u578b\u53c2\u6570\uff08\u800c\u5b83\u4eec\u662f\u9700\u8981\u4e25\u683c\u6309\u987a\u5e8f\u6392\u5217\u7684\uff09\u4e4b\u540e\u6307\u5b9a\u3002<\/p>\n
trait AssocAndParams<T, U> { type Assoc1; type Assoc2; }\n\/\/ \u7279\u6027\u7684\u987a\u5e8f\u7c7b\u578b\u53c2\u6570\u5fc5\u987b\u6309\u58f0\u660e\u987a\u5e8f\uff08\u8fd9\u91cc\u662f String \u7136\u540e\u662f usize\uff09\u3002\n\/\/ \u4e4b\u540e\u662f\u5177\u540d\u7684\u5173\u8054\u7c7b\u578b\u53c2\u6570\uff0c\u8fd9\u4e9b\u53c2\u6570\u53ef\u4ee5\u4efb\u610f\u65b9\u5f0f\u6392\u5e8f\u3002\nfn foo(d: Box<dyn AssocAndParams<String, usize, Assoc1 = i32, Assoc2 = u32>>)\n->\n    Box<dyn AssocAndParams<String, usize, Assoc2 = u32, Assoc1 = i32>>\n{\n   d\n}<\/code><\/pre>\n
2.1. \u8ba9\u5173\u8054\u7c7b\u578b\u5931\u53bb dyn<\/code> \u53ef\u7528\u6027<\/h3>\n
\u4ece Rust 1.72 \u7248\u672c\u5f00\u59cb\uff0c\u5982\u679c\u6211\u4eec\u5728\u5173\u8054\u7c7b\u578b\u4e2d\u6dfb\u52a0\u4e86 where Self: Sized<\/code> \u7ea6\u675f\uff0c\u5219\u8be5\u5173\u8054\u7c7b\u578b\u4fbf\u4e0d\u518d\u6ee1\u8db3\u5bf9\u8c61\u5b89\u5168\uff08Object safe\uff09\uff0c\u5728\u672c\u7cfb\u5217\u6587\u7ae0\u4e2d\u6211\u4eec\u79f0\u4e4b\u4e3a\u201c\u4e0d\u53ef dyn<\/code>\u201d\uff08dyn<\/code>-unusable TODO:\uff09\u3002\u5728\u8fd9\u79cd\u60c5\u51b5\u4e0b\uff0c\u867d\u7136\u6211\u4eec\u8fd8\u662f\u80fd\u591f\u4e3a\u5176 base type \u6784\u9020\u7279\u5f81\u5bf9\u8c61\uff0c\u4f46\u662f\u5728\u6784\u9020\u65f6\u4e0d\u518d\u9700\u8981\u4e3a\u5173\u8054\u7c7b\u578b\u6307\u5b9a\u5177\u540d\u53c2\u6570\uff0c\u4e14\u5728\u7279\u5f81\u5bf9\u8c61\u4e2d\u4e5f\u4e0d\u518d\u80fd\u591f\u4f7f\u7528\u8fd9\u4e2a\u5173\u8054\u7c7b\u578b\u3002<\/p>\n
trait Trait {\n    type Foo where Self: Sized;\n    fn foo(&self) -> Self::Foo where Self: Sized;\n    fn bar(&self) {}\n}\n\nimpl Trait for i32 {\n    type Foo = ();\n    fn foo(&self) -> Self::Foo {}\n}\n\nimpl Trait for u64 {\n    type Foo = f32;\n    fn foo(&self) -> Self::Foo { 0.0 }\n}\n\n\/\/ \u4e0d\u518d\u9700\u8981 `dyn Trait<Foo = ()>`!\nlet mut a: &dyn Trait = &0_i32;\n\/\/  \u8ba9\u7279\u5f81\u5bf9\u8c61\u6307\u5411\u53e6\u4e00 base type \u65f6\uff0c\u65e0\u9700\u8ba9\u5173\u8054\u7c7b\u578b\u4fdd\u6301\u4e00\u81f4\na = &0_u64;\n\/\/ \u8fd9\u4f1a\u5931\u8d25\uff0c\u56e0\u4e3a\u7c7b\u578b\u672a\u5b9a\u4e49 (`dyn Trait` \u4e0d\u53ef `Sized`)\n\/\/ let _: <dyn Trait as Trait>::Foo = todo!();<\/code><\/pre>\n
\u5728\u8fd9\u79cd\u60c5\u51b5\u4e0b\uff0c\u6211\u4eec\u8fd8\u662f\u53ef\u4ee5\u7528\u5177\u540d\u53c2\u6570\u7684\u65b9\u5f0f\u6307\u5b9a\u5173\u8054\u7c7b\u578b\uff0c\u4e0d\u8fc7\u4f1a\u62a5 warning\uff0c\u800c\u4e14\u5373\u4f7f\u8fd9\u4e48\u505a\u4e86 dyn Trait<\/code> \u4e5f\u8fd8\u662f\u65e0\u6cd5\u4f7f\u7528\u8fd9\u4e2a\u5173\u8054\u7c7b\u578b\u3002\u8bf7\u770b\u7f16\u8bd1\u5668\u7684 warning\uff1a<\/p>\n
warning: unnecessary associated type bound for not object safe associated type\n  --> src\/main.rs:24:23\n   |\n24 | let mut a: &dyn Trait<Foo = ()> = &0_i32;\n   |                                   ^^^^^^^^ help: remove this bound\n   |\n   = note: this associated type has a `where Self: Sized` bound. Thus, while the associated type can be specified, it cannot be used in any way, because trait objects are not `Sized`.\n   = note: `#[warn(unused_associated_type_bounds)]` on by default<\/code><\/pre>\n
\u4e8b\u5b9e\u4e0a\uff0c\u8fd9\u6837\u505a\u4e0d\u4ec5\u6ca1\u80fd\u6539\u53d8 dyn Trait<\/code> \u65e0\u6cd5\u4f7f\u7528\u8be5\u5173\u8054\u7c7b\u578b\u7684\u73b0\u72b6\uff0c\u8fd8\u4f1a\u5bfc\u81f4\u5bf9\u5176\u4ed6\u7c7b\u578b\u7684\u4e0d\u517c\u5bb9\uff0c\u4ece\u800c\u8fdb\u4e00\u6b65\u9650\u5236\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u7684\u53ef\u7528\u6027\uff1a<\/p>\n
let mut a: &dyn Trait<Foo = ()> = &0_i32;\n\/\/ \u4e0b\u9762\u4f1a\u5bfc\u81f4\u7f16\u8bd1\u4e0d\u901a\u8fc7\na = &0_u64;<\/code><\/pre>\n
\u4e0d\u8fc7\u8fd9\u4e5f\u5f15\u5165\u4e86\u4e00\u4e9b\u6709\u8da3\u7684\u53ef\u80fd\u6027\uff0c\u4f8b\u5982\u4e3a Box<dyn Trait><\/code> \u5b9e\u73b0\u4e0a\u9762\u7684 Trait<\/code> \u65f6\uff08TODO:\uff09\uff0c\u4e0b\u9762\u7684\u5199\u6cd5\u662f\u53ef\u4ee5\u901a\u8fc7\u7f16\u8bd1\u7684\uff1a<\/p>\n
impl<T: Default> Trait for Box<dyn Trait<Foo = T>> {\n    type Foo = T;\n    fn foo(&self) -> Self::Foo {\n        T::default()\n    }\n}<\/code><\/pre>\n
\u76ee\u524d\u7684 warning \u5199\u7684\u662f "\u867d\u7136\u53ef\u4ee5\u6307\u5b9a\u5173\u8054\u7c7b\u578b\uff0c\u4f46\u65e0\u6cd5\u4ee5\u4efb\u4f55\u65b9\u5f0f\u4f7f\u7528"\uff0c\u4f46\u8fd9\u4e2a\u4f8b\u5b50\u8868\u660e\u6280\u672f\u4e0a\u5e76\u975e\u5982\u6b64\u3002\u6211\u8ba4\u4e3a\u8fd9\u79cd\u7528\u6cd5\u53ea\u662f\u6ca1\u6709\u88ab\u9884\u6599\u5230\u3002<\/p>\n
\u5bf9\u4e8e\u8fd9\u79cd\u573a\u666f\uff0c\u7f16\u8bd1\u5668\u4e0d\u62a5 error \u800c\u662f\u62a5 warning \u7684\u539f\u56e0\u662f\uff1a\u66fe\u7ecf\u6709\u4e00\u6bb5\u65f6\u95f4\uff0c rust \u5141\u8bb8\u7528\u6237\u4e3a\u5173\u8054\u7c7b\u578b\u6dfb\u52a0 Self: Sized<\/code> \u7ea6\u675f\uff0c\u4f46\u4ecd\u7136\u9700\u8981\u5728 dyn Trait<..><\/code> \u4e2d\u663e\u5f0f\u547d\u540d\u5173\u8054\u7c7b\u578b\u3002\u56e0\u6b64\uff0c\u5c06 warning \u53d8\u6210 error \u4f1a\u662f\u4e00\u6b21\u7834\u574f\u6027\u53d8\u66f4\u3002<\/p>\n
\u9274\u4e8e\u5176\u6f5c\u5728\u7684\u5b9e\u7528\u6027\uff0c\u6211\u8ba4\u4e3a\u81f3\u5c11\u5e94\u8be5\u4fee\u6539\u8fd9\u4e2a warning \u7684\u63aa\u8f9e\uff0c\u751a\u81f3\u8003\u8651\u91cd\u65b0\u547d\u540d\u3002<\/p>\n
3. \u5d4c\u5957\u7684\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u662f\u4e0d\u53ef\u884c\u7684<\/h2>\n
\u5bf9\u975e\u5b9a\u957f\u7c7b\u578b\uff08unsized\uff09\u7684\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u9700\u8981\u7ecf\u8fc7\u4e00\u4e2a\u95f4\u63a5\u5c42\uff08\u4f8b\u5982\u5f15\u7528\u6216 Box<\/code>\uff09\u624d\u53ef\u884c\uff0c\u8fd9\u662f\u56e0\u4e3a\u9700\u8981\u5bb9\u7eb3\u6307\u5411\u865a\u8868\u7684\u5bbd\u6307\u9488\uff0c\u800c\u4e14 rust \u4e5f\u4e0d\u5141\u8bb8 move \u4e00\u4e2a\u975e\u5b9a\u957f\u7c7b\u578b\u3002<\/p>\n
\u7136\u800c\uff0c\u5982\u679c\u6709\u591a\u4e2a\u95f4\u63a5\u5c42\u5d4c\u5957\uff0c\u90a3\u4e48\u7f16\u8bd1\u5668\u5c31\u4e0d\u80fd\u6267\u884c\u8fd9\u79cd\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u4e86\u3002\u4f8b\u5982\uff0c\u6211\u4eec\u4e0d\u80fd\u5c06 Vec<Box<T>><\/code> \u5f3a\u5236\u8f6c\u6362\u4e3a Vec<Box<dyn Trait>><\/code>\u3002\u8fd9\u662f\u56e0\u4e3a Box<T><\/code> \u548c Box<dyn Trait><\/code> \u6709\u4e0d\u540c\u7684\u5185\u5b58\u5e03\u5c40\uff0c\u524d\u8005\u5360\u7528\u7684\u5185\u5b58\u7a7a\u95f4\u5c31\u662f\u4e00\u4e2a\u6307\u9488\u7684\u5927\u5c0f\uff0c\u800c\u540e\u8005\u5219\u662f\u4e24\u4e2a\u6307\u9488\u7684\u5927\u5c0f\u3002\u6240\u4ee5\uff0c\u6574\u4e2a Vec<\/code> \u90fd\u9700\u8981\u91cd\u65b0\u5206\u914d\u5185\u5b58\u4ee5\u9002\u5e94\u8fd9\u6837\u7684\u53d8\u5316\uff1a<\/p>\n
fn convert_vec<'a, T: Trait + 'a>(v: Vec<Box<T>>) -> Vec<Box<dyn Trait + 'a>> {\n    v.into_iter().map(|bx| bx as _).collect()\n}<\/code><\/pre>\n
\u901a\u5e38\u60c5\u51b5\u4e0b\uff0c\u975e\u5b9a\u957f\u7c7b\u578b\u7684\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u4f1a\u6d88\u8017\uff08consume\uff09\u6389\u539f\u59cb\u7684\u6307\u9488\uff08\u5f15\u7528\u3001Box<\/code> \u7b49\uff09\uff0c\u5e76\u4ea7\u751f\u4e00\u4e2a\u65b0\u7684\u6307\u9488\uff0c\u800c\u8fd9\u5728\u591a\u5c42\u5d4c\u5957\u7684\u573a\u666f\u4e0b\u662f\u65e0\u6cd5\u53d1\u751f\u7684\u3002<\/p>\n
\u4ece\u7f16\u8bd1\u5668\u5185\u90e8\u89c6\u89d2\u6765\u8bf4\uff0c\u54ea\u4e9b\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u662f\u53ef\u80fd\u7684\u53d6\u51b3\u4e8e CoerceUnsized<\/code> \u7279\u5f81<\/a>\uff0c\u4ee5\u53ca\u7531\u7f16\u8bd1\u5668\u5b9e\u73b0\u7684 Unsize<\/code> \u7279\u5f81\uff0c\u6b63\u5982\u94fe\u63a5\u4e2d\u7684\u6587\u6863\u91cc\u8ba8\u8bba\u7684\u90a3\u6837\u3002<\/p>\n
3.1. \u4e00\u4e9b\u4f8b\u5916<\/h3>\n
\u4e8b\u5b9e\u4e0a\uff0c\u6709\u4e00\u4e9b\u4f8b\u5916\u60c5\u51b5\uff1a\u5bf9\u4e8e\u4e00\u4e9b\u7279\u522b\u7684\u95f4\u63a5\u5c42\uff0c\u5373\u4f7f\u53d1\u751f\u4e86\u5d4c\u5957\uff0c\u4e5f\u4f9d\u7136\u53ef\u4ee5\u8fdb\u884c\u975e\u5b9a\u957f\u7c7b\u578b\u7684\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u3002<\/p>\n
\u5982\u679c\u4f60\u9605\u8bfb\u4e86\u4e0a\u9762\u94fe\u63a5\u4e2d\u7684\u6587\u7ae0\uff0c\u4f1a\u53d1\u73b0\u6709\u4e9b\u7c7b\u578b\uff0c\u6bd4\u5982 Cell<\/code>\uff0c\u4ee5\u9012\u5f52\u7684\u65b9\u5f0f\u5b9e\u73b0\u4e86 CoerceUnsized<\/code>\u3002\u8fd9\u662f\u56e0\u4e3a\u8fd9\u4e9b\u7c7b\u578b\uff08\u5305\u62ec Cell<\/code>\uff0cRefCell<\/code>\uff0cSyncUnsafeCell<\/code>\uff0cUnsafeCell<\/code>\uff09\u4e0e\u5b83\u4eec\u7684\u6cdb\u578b\u53c2\u6570\u6709\u76f8\u540c\u7684\u5185\u5b58\u5e03\u5c40\u3002\u56e0\u6b64\uff0c\u5728\u5916\u4fa7\u518d\u5305\u4e0a\u4e00\u5c42 Cell<\/code> \u4e0d\u4f1a\u88ab\u89c6\u4e3a\u662f\u201c\u5d4c\u5957\u201d\u7684\u3002<\/p>\n
\/\/ \u5931\u8d25 :-(\n\/\/fn coerce_vec<'a, T: Trait + 'a>(v: Vec<Box>) -> Vec<Box<dyn Trait + 'a>> {\n\/\/ v\n\/\/}\n\/\/ \u6210\u529f\uff01:-)\nfn coerce_cell<'a, T: Trait + 'a>(c: Cell<Box>) -> Cell<Box<dyn Trait + 'a>> {\nc\n}<\/code><\/pre>\n
\u6211\u4eec\u5c06\u5728\u63a5\u4e0b\u6765\u7684\u7ae0\u8282\uff08TODO:\uff09\u8bb2\u89e3\u90a3\u4e9b\u8868\u9762\u4e0a\u7684\u4f8b\u5916\u60c5\u51b5\uff08\u5176\u5b9e\u53ea\u662f supertype \u5f3a\u5236\u8f6c\u6362\uff09\u3002<\/p>\n
4. Sized<\/code> \u7684\u9650\u5236<\/h2>\n
\u4efb\u4f55\u4e00\u4e2a base type \uff0c\u5fc5\u987b\u662f\u5b9a\u957f\u7c7b\u578b\uff08Sized<\/code>\uff09\uff0c\u624d\u80fd\u88ab\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u4e3a dyn Trait<\/code>\u3002\u4f8b\u5982\uff0c\u5c3d\u7ba1 str<\/code> \u5b9e\u73b0\u4e86 Display<\/code>\uff0c\u4f46\u7531\u4e8e\u5b83\u662f\u975e\u5b9a\u957f\u7c7b\u578b\uff08unsized\uff09\uff0c &str<\/code> \u4fbf\u4e0d\u80fd\u88ab\u5f3a\u5236\u8f6c\u6362\u4e3a &dyn Display<\/code>\u3002<\/p>\n
\u4e3a\u4ec0\u4e48\u4f1a\u6709\u8fd9\u4e2a\u9650\u5236\u5462\uff1f\u4e8b\u5b9e\u4e0a\uff0c&str<\/code> \u672c\u8eab\u4e5f\u662f\u4e00\u4e2a\u5bbd\u6307\u9488\uff0c\u5b83\u5305\u542b\u4e00\u4e2a\u6307\u5411 UTF8 \u5b57\u8282\u7684\u6307\u9488\uff0c\u548c\u4e00\u4e2a usize<\/code>\uff0c\u8868\u793a\u5b57\u8282\u7684\u6570\u91cf\u3002\u7c7b\u4f3c\u5730\uff0c\u5207\u7247\u5f15\u7528 &[T]<\/code> \u5305\u542b\u4e00\u4e2a\u6307\u5411\u8fde\u7eed\u6570\u636e\u7684\u6307\u9488\uff0c\u548c\u4e00\u4e2a\u8868\u793a\u5143\u7d20\u6570\u91cf\u7684\u8ba1\u6570\u3002<\/p>\n
\u7531\u6b64\u89c2\u4e4b\uff0c\u5982\u679c\u8981\u4ece &str<\/code> \u6216 &[T]<\/code> \u521b\u5efa\u7279\u5f81\u5bf9\u8c61\uff0c\u90a3\u4e48\u8fd9\u4e2a\u7279\u5f81\u5bf9\u8c61\u7684\u5185\u5b58\u5e03\u5c40\u4f3c\u4e4e\u9700\u8981\u53d8\u6210\u4e00\u4e2a\u542b\u6709\u4e09\u4e2a\u6210\u5458\u7684\u201c\u8d85\u5bbd\u6307\u9488\u201d\uff1a\u4e00\u4e2a\u6307\u5411\u6570\u636e\u7684\u6307\u9488\u3001\u4e00\u4e2a\u5143\u7d20\u8ba1\u6570\u548c\u4e00\u4e2a\u865a\u8868\u6307\u9488\u3002\u4f46\u5bf9\u4e8e\u7f16\u8bd1\u5668\u800c\u8a00\uff0c&dyn Trait<\/code> \u662f\u4e00\u79cd\u5177\u4f53\u7684\u7c7b\u578b\uff0c\u56e0\u6b64\u5b83\u6709\u7740\u786e\u5b9a\u7684\u7ed3\u6784\uff0c\u53ea\u5305\u542b\u4e24\u4e2a\u6307\u9488\u3002\u6240\u4ee5\uff0c\u201c\u8d85\u5bbd\u6307\u9488\u201d\u8fd9\u79cd naive \u7684\u8bbe\u60f3\u662f\u4e0d\u53ef\u884c\u7684\u3002\u800c\u4e14\uff0c\u8fd9\u79cd\u8bbe\u60f3\u8fd8\u6709\u53e6\u4e00\u4e2a\u95ee\u9898\uff1a\u5982\u679c\u6211\u4eec\u60f3\u5bf9\u4e00\u4e2a\u201c\u8d85\u5bbd\u6307\u9488\u201d\u8fdb\u884c\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\uff0c\u90a3\u4f1a\u53d1\u751f\u4ec0\u4e48\u5462\uff1f\u53ef\u4ee5\u60f3\u8c61\uff0c\u6bcf\u6b21\u8fdb\u884c\u9012\u5f52\u7684\u8f6c\u6362\u65f6\u90fd\u4f1a\u5f15\u5165\u4e00\u4e2a\u65b0\u7684\u6307\u9488\uff0c\u4f7f\u5f97\u5176\u5185\u5b58\u53d8\u5f97\u65e0\u9650\u5927\u3002<\/p>\n
\u4e00\u79cd\u4e0d\u90a3\u4e48 naive \u7684\u65b9\u6cd5\u662f\u5728\u52a8\u6001\u5206\u53d1\u673a\u5236\u4e0a\u505a\u6539\u52a8\uff0c\u5bf9\u8fd9\u4e9b Unsized \u7684 base type \u505a\u4e13\u95e8\u7684\u5904\u7406\u3002\u4e3e\u4e2a\u4f8b\u5b50\uff0c\u5728\u7c7b\u578b\u8f6c\u6362\u8fc7\u7a0b\u4e2d\uff0c\u4e00\u65e6\u64e6\u9664\u4e86 str<\/code> \u7c7b\u578b\uff0c\u6211\u4eec\u5c31\u4e22\u5931\u4e86\u4e00\u4e9b\u4fe1\u606f\uff1a\u4f8b\u5982 &str<\/code> \u4e5f\u662f\u4e00\u79cd\u5bbd\u6307\u9488\uff0c\u4ee5\u53ca\u521b\u5efa\u8fd9\u79cd\u5bbd\u6307\u9488\u7684\u65b9\u6cd5\u3002\u7136\u800c\uff0c\u7f16\u8bd1\u5668\u53c8\u9700\u8981\u91cd\u65b0\u521b\u5efa\u4e00\u4e2a\u5bbd\u6307\u9488\uff0c\u624d\u80fd\u8fdb\u884c\u52a8\u6001\u5206\u53d1\u3002<\/p>\n
\u56e0\u6b64\uff0c\u5982\u679c\u8981\u8ba9\u7f16\u8bd1\u5668\u652f\u6301\u6784\u5efa Unsized \u7684\u7279\u5f81\u5bf9\u8c61\uff0c\u90a3\u4e48\u5728\u6784\u5efa\u6307\u5411 base type \u7684\u6307\u9488\u65f6\uff0c\u4e8b\u60c5\u5c31\u4f1a\u53d8\u5f97\u5f88\u590d\u6742\u3002\u9996\u5148\uff0c\u6211\u4eec\u9700\u8981\u4e3a\u666e\u901a\u7684\u7a84\u6307\u9488\u8bbe\u8ba1\u4e00\u79cd\u5904\u7406\u903b\u8f91\uff1b\u5176\u6b21\uff0c\u5bf9\u4e8e\u60f3\u8981\u652f\u6301\u7684\u6bcf\u79cd\u5bbd\u6307\u9488\u7c7b\u578b\uff0c\u6211\u4eec\u90fd\u8981\u989d\u5916\u5f15\u5165\u4e00\u6bb5\u4e13\u95e8\u7684\u5904\u7406\u903b\u8f91\u3002\u4e0d\u6b62\u5982\u6b64\uff0c\u5173\u952e\u7684\u5143\u6570\u636e\uff08\u6bd4\u5982 str<\/code> \u7684\u957f\u5ea6\uff09\u4e5f\u5fc5\u987b\u627e\u5730\u65b9\u5b58\u653e\u8d77\u6765\uff0c\u800c\u4e14\u8fd8\u4e0d\u80fd\u50cf\u865a\u8868\u90a3\u6837\u653e\u5728\u5185\u5b58\u91cc\u7684 .data \u6bb5\uff08\u9759\u6001\u5185\u5b58\uff09\u4e2d\u3002<\/p>\n
\u8fd9\u5c06\u4f1a\u662f\u5730\u72f1\u822c\u7684\u590d\u6742\uff0c\u56e0\u6b64 rust \u7684\u8bbe\u8ba1\u8005\u4eec\u51b3\u5b9a\u7d22\u6027\u4e0d\u652f\u6301 Unsized \u7684 base type \u4e86\u3002<\/p>\n
\u4e0d\u8fc7\u6709\u65f6\u5019\uff0c\u4f60\u53ef\u4ee5\u901a\u8fc7\u4f8b\u5982\u4e3a &str<\/code> \u800c\u4e0d\u662f str<\/code> \u5b9e\u73b0\u7279\u5f81\uff0c\u7136\u540e\u5c06 &'_ str<\/code> \u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u4e3a dyn Trait + '_<\/code> \u6765\u7ed5\u8fc7\u8fd9\u4e2a\u9650\u5236\uff0c\u56e0\u4e3a\u5f15\u7528\u662f\u4e00\u79cd\u5b9a\u957f\u7c7b\u578b\u3002<\/p>\n
\/\/ \u8fd9\u6bb5\u4ee3\u7801\u4e0d\u80fd\u901a\u8fc7\u7f16\u8bd1\uff0c\u56e0\u4e3a str \u662f\u975e\u5b9a\u957f\u7c7b\u578b\uff0c\n\/\/ \u6240\u4ee5\u6211\u4eec\u4e0d\u80fd\u5c06 str \u5f3a\u5236\u8f6c\u6362\u4e3a dyn Display\uff0c\n\/\/ \u56e0\u800c\u65e0\u6cd5\u5c06 &str \u5f3a\u5236\u8f6c\u6362\u4e3a &dyn Display\u3002\n\/\/ let _: &dyn Display = "hi";\n\n\/\/ \u7136\u800c\uff0c&str \u4e5f\u5b9e\u73b0\u4e86 Display\u3002\uff08\u5982\u679c\u6709 T: Display\uff0c\u90a3\u4e48 &T: Display\uff09\u3002\n\/\/ \u7531\u4e8e &str \u662f\u5b9a\u957f\u7c7b\u578b\uff08Sized\uff09\uff0c\u6211\u4eec\u5c31\u80fd\u5c06 &&str \u5f3a\u5236\u8f6c\u6362\u4e3a &dyn Display\uff1a\nlet _: &dyn Display = &"hi";<\/code><\/pre>\n
\u5b9a\u957f\u7c7b\u578b\uff08Sized<\/code>\uff09\u4e5f\u88ab\u7528\u4f5c\u67d0\u79cd\u201c\u975e-dyn\u201d\u7684\u6807\u8bc6\uff0c\u8fd9\u4e00\u70b9\u6211\u4eec\u7a0d\u540e\uff08TODO:\uff09\u4f1a\u8fdb\u4e00\u6b65\u63a2\u8ba8\u3002<\/p>\n
\u5728 dyn Trait<\/code> \u81ea\u8eab\u7684\u4e0d\u540c\u5f62\u5f0f\u95f4\u8fdb\u884c\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u65f6\uff0c\u4f1a\u51fa\u73b0\u4e00\u79cd\u5e38\u89c1\u7684\u5f02\u5e38\uff0c\u800c\u5b83\u6b63\u662f\u4e0e Size<\/code> \u9650\u5236\u6709\u5173\u3002\u6211\u4eec\u4f1a\u5728\u4e0b\u6587\u8ba8\u8bba\u8fd9\u4e2a\u60c5\u51b5\u3002<\/p>\n
5. \u5220\u9664\u81ea\u52a8\u7279\u5f81\uff08auto trait\uff09<\/h2>\n
\u6211\u4eec\u53ef\u4ee5\u5c06 dyn Trait + Send<\/code> \u5f3a\u5236\u8f6c\u6362\u4e3a dyn Trait<\/code>\uff0c\u5e76\u4ee5\u7c7b\u4f3c\u7684\u65b9\u5f0f\u4e22\u5f03\u4efb\u4f55\u5176\u4ed6\u81ea\u52a8\u7279\u5f81\u3002<\/p>\n
\u867d\u7136 dyn Trait<\/code> \u4e0d\u662f dyn Trait + Send<\/code> \u7684\u8d85\u7c7b\u578b\uff08super type\uff09\uff0c\u4f46\u8fd9\u4ecd\u7136\u88ab\u79f0\u4e3a\u5c06 dyn Trait + Send<\/code> \u5411\u4e0a\u8f6c\u6362\uff08upcasting\uff09\u4e3a dyn Trait<\/code>\u3002<\/p>\n
\u8bf7\u6ce8\u610f\uff0c\u81ea\u52a8\u7279\u5f81\u4e0d\u62e5\u6709\u65b9\u6cd5\uff0c\u56e0\u6b64\u8fd9\u4e9b\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u65e0\u9700\u5bf9\u865a\u8868\u8fdb\u884c\u4efb\u4f55\u66f4\u6539\u3002\u8fd9\u6837\u4e00\u6765\uff0crust \u5141\u8bb8\u7528\u4e8e\u4ece\u4e00\u4e2a\u8f83\u4e25\u683c\u7684\u51fd\u6570\uff08\u4f8b\u5982\u8981\u6c42 dyn Trait + Send<\/code> \u7684\u51fd\u6570\uff09\u8c03\u7528\u4e00\u4e2a\u9650\u5236\u8f83\u5c11\u7684\u51fd\u6570\uff08\u63a5\u53d7 dyn Trait<\/code> \u7684\u51fd\u6570\uff09\u3002\u8fd9\u79cd\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u662f\u5fc5\u8981\u7684\uff0c\u56e0\u4e3a\u5b83\u4eec\u662f\u4e0d\u540c\u7684\u5177\u4f53\u7c7b\u578b\uff0c\u800c\u4e0d\u662f\u6cdb\u578b\u3001\u5b50\u7c7b\u578b\u6216\u52a8\u6001\u7c7b\u578b\u3002<\/p>\n
\u4e0d\u8fc7\uff0c\u5373\u4f7f\u4e0d\u9700\u8981\u4fee\u6539\u865a\u8868\uff0c\u8fd9\u79cd\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u4f9d\u7136\u4e0d\u53ef\u7528\u4e8e\u5d4c\u5957\u573a\u666f\u3002<\/p>\n
6. \u53cd\u8eab\u8f6c\u6362\uff08reflexive\uff09<\/h2>\n
\u4e0b\u9762\u6211\u8981\u8bf4\u4e00\u6761\u770b\u8d77\u6765\u662f\u5e9f\u8bdd\u7684\u89c4\u5219\uff1a\u4f60\u53ef\u4ee5\u5c06 dyn Trait<\/code> \u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u4e3a dyn Trait<\/code>\u3002<\/p>\n
\u5b9e\u9645\u4e0a\u5b83\u7684\u672c\u610f\u662f\uff1a\u4f60\u53ef\u4ee5\u5c06 dyn Trait + 'a<\/code> \u5f3a\u5236\u8f6c\u6362\u4e3a dyn Trait + 'b<\/code>\uff0c\u5176\u4e2d 'a: 'b<\/code>\u3002\u8fd9\u5bf9\u4e8e dyn Trait + '_<\/code> \u7684\u501f\u7528\u673a\u5236\u8d77\u5230\u4e86\u91cd\u8981\u4f5c\u7528\u3002<\/p>\n
\u5728\u7f16\u8bd1\u8fc7\u7a0b\u4e2d\uff0c\u751f\u547d\u5468\u671f\u4f1a\u88ab\u64e6\u9664\uff0c\u56e0\u6b64\u865a\u8868\u5728\u4efb\u4f55\u751f\u547d\u5468\u671f\u4e0b\u90fd\u662f\u76f8\u540c\u7684\u3002\u5c3d\u7ba1\u5982\u6b64\uff0c\u8fd9\u79cd Unsized \u7684\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u4f9d\u7136\u4e0d\u53ef\u7528\u4e8e\u5d4c\u5957\u573a\u666f\u3002<\/p>\n
\u7136\u800c\u5728\u672a\u6765\u7684\u7ae0\u8282\uff08TODO:\uff09\u4e2d\uff0c\u6211\u4eec\u5c06\u770b\u5230\uff0c\u5373\u4f7f\u5728\u5d4c\u5957\u7684\u60c5\u51b5\u4e0b\uff0c\u534f\u53d8\uff08variance\uff09\u4e5f\u53ef\u4ee5\u7f29\u77ed\u7279\u5f81\u5bf9\u8c61\u7684\u751f\u547d\u5468\u671f\uff0c\u524d\u63d0\u662f\u8be5\u5d4c\u5957\u4e5f\u662f\u534f\u53d8\u7684\u3002\u7d27\u63a5\u7740\u7684\u5173\u4e8e\u9ad8\u9636\u7c7b\u578b\u7684\u7ae0\u8282\uff08TODO:\uff09\u5c06\u63a2\u8ba8\u53e6\u4e00\u79cd\u4e0e\u751f\u547d\u5468\u671f\u76f8\u5173\u7684\u5f3a\u5236\u8f6c\u6362\uff0c\u4e5f\u53ef\u4ee5\u88ab\u89c6\u4e3a\u662f\u53cd\u8eab\u7684\u3002<\/p>\n
7. \u8d85\u7c7b\u578b\u7684 upcast<\/h2>\n
\u867d\u7136\u76ee\u524d\u5728 rust \u7a33\u5b9a\u7248\u4e2d\u8fd8\u4e0d\u652f\u6301\uff0c\u4f46\u4ece dyn SubTrait<\/code> \u5411 dyn SuperTrait<\/code> \u8fdb\u884c\u5411\u4e0a\u8f6c\u6362\uff08upcast\uff09\u7684\u529f\u80fd\u9884\u8ba1\u5728\u672a\u6765\u67d0\u4e00\u5929\u4f1a\u5b9e\u73b0\u3002<\/p>\n
\u518d\u6b21\u5f3a\u8c03\uff0c\u8fd9\u660e\u786e\u662f\u4e00\u79cd\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\uff0c\u800c\u975e\u5b50\u7c7b\u578b\u4e0e\u8d85\u7c7b\u578b\u7684\u5173\u7cfb\uff08\u5c3d\u7ba1\u672f\u8bed\u5982\u6b64\uff09\u3002\u5c3d\u7ba1\u8fd9\u662f\u4e00\u4e2a\u5177\u4f53\u7684\u5b9e\u73b0\u7ec6\u8282\uff0c\u4f46\u4e0e\u524d\u51e0\u4e2a\u793a\u4f8b\u76f8\u53cd\uff0c\u8fd9\u79cd\u8f6c\u6362\u53ef\u80fd\u4f1a\u6d89\u53ca\u66ff\u6362\u865a\u8868\u6307\u9488\u3002<\/p>\n
\u5728\u8be5\u529f\u80fd\u5c1a\u672a\u7a33\u5b9a\u4e4b\u524d\uff0c\u4f60\u53ef\u4ee5\u624b\u52a8\u5b9e\u73b0\u8d85\u7c7b\u578b\u5411\u4e0a\u8f6c\u6362\u903b\u8f91\u3002<\/p>\n
8. \u4ec5\u9002\u7528\u4e8e\u5bf9\u8c61\u5b89\u5168\u7684\u7279\u5f81<\/h2>\n
\u5728\u4f7f\u7528\u7279\u5f81\u5bf9\u8c61\u65f6\uff0c\u5bf9\u4e8e\u7279\u5f81\u8fd8\u6709\u5176\u4ed6\u9650\u5236\uff0c\u6211\u4eec\u5728\u8fd9\u91cc\u5c1a\u672a\u8ba8\u8bba\uff0c\u6bd4\u5982\u76ee\u524d\u8fd8\u4e0d\u652f\u6301\u5177\u6709\u5173\u8054\u6cdb\u578b\u7c7b\u578b\uff08GATs, Generic Associated Types\uff09\u7684\u7279\u5f81\u3002\u6211\u4eec\u5728\u4e0b\u4e00\u8282\uff08TODO:\uff09\u4e2d\u4f1a\u8be6\u7ec6\u4ecb\u7ecd\u8fd9\u4e9b\u5185\u5bb9\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
\u672c\u6587\u662f rust \u793e\u533a\u5927\u795e quinedot \u7684\u7cfb\u5217\u6587\u7ae0 \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 […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8],"tags":[24,30],"class_list":["post-348","post","type-post","status-publish","format-standard","hentry","category-rust","tag-rust","tag-30"],"_links":{"self":[{"href":"https:\/\/cococat.top\/index.php\/wp-json\/wp\/v2\/posts\/348","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/cococat.top\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/cococat.top\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/cococat.top\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/cococat.top\/index.php\/wp-json\/wp\/v2\/comments?post=348"}],"version-history":[{"count":0,"href":"https:\/\/cococat.top\/index.php\/wp-json\/wp\/v2\/posts\/348\/revisions"}],"wp:attachment":[{"href":"https:\/\/cococat.top\/index.php\/wp-json\/wp\/v2\/media?parent=348"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/cococat.top\/index.php\/wp-json\/wp\/v2\/categories?post=348"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/cococat.top\/index.php\/wp-json\/wp\/v2\/tags?post=348"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}