downcast
trait T ãå®è£ ãã struct S ã«ã¤ãã¦ã S ãã &dyn T ã¸ã¢ãããã£ã¹ãããå¾ã &dyn T ãã &S ã¸ãã¦ã³ãã£ã¹ãã§ãâ¦ã¾ãããRustã§traitç¶æ¿ã®dynãªãªãã¸ã§ã¯ããæ±ããã¨ããã¨æ²ãããã¤ã³ãã§ãã trait T { fn hello(&self); } struct S {} impl â¦