创建新泛型结构的正确方法是什么? [英] What is the proper way to create a new generic struct?

问题描述

我正在尝试创建一个可以初始化为 T 类型的通用结构.看起来像这样:

  pub struct MyStruct< T>{test_field:选项< T> ;，名称:字符串，年龄:i32，}impl MyStruct< T>{fn new(new_age:i32，new_name:String)->MyStruct< T>{MyStruct< T>{test_field:无，年龄:new_age，名称:new_name，}}} 

这似乎不起作用.除其他错误外，我得到:

 错误:链接的比较运算符需要括号->src/lib.rs:9:17|9 |MyStruct< T>{|^^^^^| 

解决方案

我强烈推荐阅读 Rust编程语言 .它涵盖了这样的基础知识，Rust团队花费了大量时间来使其变得更好！具体来说，关于泛型的部分可能会在这里有所帮助./p>

实例化结构时，您无需使用< T> .将推断出 T 的类型.您需要在 impl 块上声明 T 是通用类型:

  struct MyStruct< T>{test_field:选项< T> ;，名称:字符串，年龄:i32，}impl TMyStruct< T>{//^^^fn new(new_age:i32，new_name:String)->MyStruct< T>{MyStruct {test_field:无，年龄:new_age，名称:new_name，}}} 

作为 = help:如果要指定类型参数，请使用`::< ...>`代替`< ...>`= help:或如果要指定fn参数，则使用`(...)`

我只在类型不明确时才看到这样的事情，这种情况很少发生.

I'm trying to make a generic struct that can be initialized to something of type T. It looks like this:

pub struct MyStruct<T> {
    test_field: Option<T>,
    name: String,
    age: i32,
}

impl MyStruct<T> {
    fn new(new_age: i32, new_name: String) -> MyStruct<T> {
        MyStruct<T> {
            test_field: None,
            age: new_age,
            name: new_name,
        }
    }
}

This doesn't seem to work. Among other errors, I get:

error: chained comparison operators require parentheses
 --> src/lib.rs:9:17
  |
9 |         MyStruct<T> {
  |                 ^^^^^
  |

解决方案

I highly recommend reading The Rust Programming Language. It covers basics like this, and the Rust team spent a lot of time to make it good! Specifically, the section on generics would probably have helped here.

You don't need to use <T> when instantiating the struct. The type for T will be inferred. You will need to declare that T is a generic type on the impl block:

struct MyStruct<T> {
    test_field: Option<T>,
    name: String,
    age: i32,
}

impl<T> MyStruct<T> {
//  ^^^
    fn new(new_age: i32, new_name: String) -> MyStruct<T> {
        MyStruct {
            test_field: None,
            age: new_age,
            name: new_name,
        }
    }
}

As DK. points out, you could choose to specify the type parameter using the turbofish syntax (::<>):

MyStruct::<T> {
//      ^^^^^
    test_field: None,
    age: new_age,
    name: new_name,
}

Modern compiler versions actually tell you this now:

  = help: use `::<...>` instead of `<...>` if you meant to specify type arguments
  = help: or use `(...)` if you meant to specify fn arguments

I've only ever seen something like this when the types are ambiguous, which doesn't happen very often.

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