#![feature(core_intrinsics)] fn print_type_of<T>(_: T) { println!("{}", unsafe { std::intrinsics::type_name::<T>() }); } fn main() { let ref a: i32; a = &1; let ref a: i32 = 1; print_type_of(a); let c: &u32 = &&&&&2; print_type_of(c); }
上面2个a的类型都是&i32
enum带参数时使用match会move走enum的参数，如下这样写会报错
#![feature(core_intrinsics)] fn print_type_of<T>(_: T) { println!("{}", unsafe { std::intrinsics::type_name::<T>() }); } fn main() { let os = Some(String::from("s")); match os { Some(s) => { print_type_of(s); }, _ => () }; println!("{:?}", os); }
改下match的参数匹配模式，用ref来匹配就不会出错了
#![feature(core_intrinsics)] fn print_type_of<T>(_: T) { println!("{}", unsafe { std::intrinsics::type_name::<T>() }); } fn main() { let os = Some(String::from("s")); match os { Some(ref s) => { print_type_of(s); // s此时是&alloc::string::String类型 }, _ => () }; println!("{:?}", os); }
如果match的对象是一个引用，会发现参数是引用类型，比如
#![feature(core_intrinsics)] fn print_type_of<T>(_: T) { println!("{}", unsafe { std::intrinsics::type_name::<T>() }); } fn main() { let os = &Some(String::from("s")); match os { Some(s) => { print_type_of(s); }, _ => () }; }
打印的是&alloc::string::String
其实和下面的代码一样
#![feature(core_intrinsics)] fn print_type_of<T>(_: T) { println!("{}", unsafe { std::intrinsics::type_name::<T>() }); } fn main() { let os = &Some(String::from("s")); match os { &Some(ref s) => { print_type_of(s); }, _ => () }; }
原文：https://www.cnblogs.com/chen8840/p/12699265.html