我有以下代码:
extern crate futures; // 0.1.24
use futures::Future;
use std::io;
struct Context;
pub trait MyTrait {
fn receive(context: Context) -> Future<Item = (), Error = io::Error>;
}
pub struct MyStruct {
my_trait: MyTrait,
}
当我尝试编译它时,我收到错误消息:
error[E0038]: the trait `MyTrait` cannot be made into an object
--> src/lib.rs:13:5
|
13 | my_trait: MyTrait,
| ^^^^^^^^^^^^^^^^^ the trait `MyTrait` cannot be made into an object
|
= note: method `receive` has no receiver
我想我知道它为什么会发生,但我如何从结构中引用特征呢？可能吗？也许还有其他方法可以实现相同的行为？
我有各种结构,都实现相同的特征.我想在某些条件下进行分支,在运行时决定实例化哪些结构.然后,无论我遵循哪个分支,我都想从该特征中调用方法.
这可能在Rust吗？我希望实现类似下面的内容(不编译):
trait Barks {
fn bark(&self);
}
struct Dog;
impl Barks for Dog {
fn bark(&self) {
println!("Yip.");
}
}
struct Wolf;
impl Barks for Wolf {
fn bark(&self) {
println!("WOOF!");
}
}
fn main() {
let animal: Barks;
if 1 == 2 {
animal = Dog;
} else {
animal = Wolf;
}
animal.bark();
}
我有这个简化的Rust代码:
use std::io::Result;
pub trait PacketBuffer {}
pub trait DnsRecordData {
fn write<T: PacketBuffer>(&self, buffer: &mut T) -> Result<usize>;
}
pub struct DnsRecord<R: DnsRecordData + ?Sized> {
pub data: Box<R>,
}
pub struct DnsPacket {
pub answers: Vec<DnsRecord<dyn DnsRecordData>>,
}
目的是DnsRecord应该能够保存任何实现DnsRecordData特征的结构,其中不同的结构代表A,AAAA,CNAME等.
这失败并出现错误:
error[E0038]: the trait `DnsRecordData` cannot be made into an object
--> src/lib.rs:14:5
|
14 | pub answers: Vec<DnsRecord<dyn DnsRecordData>>,
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `DnsRecordData` cannot be made into an object
|
= note: method …我正在努力解决对象安全的基础问题.如果我有这个代码
struct S {
x: i32
}
trait Trait: Sized {
fn f(&self) -> i32 where Self: Sized;
}
fn object_safety_dynamic(x: Trait) {}
我收到
fn object_safety_dynamic(x: Trait) {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `traits::Trait` cannot be made into an object
= note: the trait cannot require that `Self : Sized`
当添加/更改:Sized为特征的继承或f绑定时,我收到稍微不同的错误消息.
有人能解释一下:
为什么这个特定的例子不起作用？Trait Objects一章说明"那么什么使方法对象安全？每种方法都必须要求Self: Sized".那不是满满的吗？
Trait: Sized和之间有什么区别where Self: Sized？(嗯,是的,一个继承了特性,另一个是参数绑定,但是从Rust的特质对象的角度来看？
我必须做的首选改变是什么object_safety_dynamic？
rustc 1.19.0-nightly (01951a61a 2017-05-20) …