Trait
1. Concept
1.Trait concept
Trait is what a certain type has and can share functions with other types. It abstracts the shared behavior between types. Trait bounds refers to the generic type parameter specified as a type that implements a specific behavioral constraint.
2. The role of traits
- Used as an interface.
- The type marks Copy, Sized, and the IDE can recognize some fixed types of behaviors through the type marks.
- Generic constraints, input parameters, and output parameters act as generic constraints.
- Abstract types are equivalent to dynamic language calls, static calls, dynamic calls, and dynamic distribution.
3. The concept is similar to the virtual function of C++, the difference is that rust does not have the concept of class inheritance.
1. Use Trait as an interface
1. Definition of Trait
//使用关键字trait把方法签名放在一起，来定义实现某种目的必须的一组行为
//这里使用文章做例子，所有的文章都有标题和作者，不管是博客还是论文
pub trait Article
{
//只有方法签名，没有具体实现，可以有多个方法
fn digest(&self) ->String;
//默认实现
fn aothor(&self)
{
println!("默认实现");
}
}
2. Implement Traits
pub struct WeChatArticle
{
pub aothor : String,//作者
pub title : String,//标题
pub timestamp : String//创建时间戳
}
pub struct Blog
{
pub aothor : String,//作者
pub title : String,//标题
pub collect : u64//收藏个数
}
//为类型实现trait
impl Article for Blog
{
fn digest(&self) ->String
{
self.title.clone() + &self.title.clone() + &self.collect.to_string()
}
}
impl Article for WeChatArticle
{
fn digest(&self) ->String
{
self.title.clone() + &self.title.clone() + &self.timestamp.clone()
}
}
3. use
use rust_demo::Blog;
use rust_demo::Article;
fn main()
{
let blog : Blog = Blog
{
aothor:"matt".to_string(),
title:"Rust Trait 的应用".to_string(),
collect: 20
};
println!("Blog aothor is {}",blog.digest());
}s
4. The default implementation of Trait
pub trait article
{
//这个为Trait的默认实现，如果类型没有重写这个方法，则使用默认实现
fn aothor(&self) ->String
{
self.aothor.clone()
}
fn title(&self) ->String;
}
2. Trai is used as a parameter
1. Passed in as parameters
//item是实现了Article这个Trait的类型
pub fn notify(item : impl Article)
{
print!("Article digest {} \n",item.digest());
}
use
fn main()
{
let blog : Blog = Blog
{
aothor:"matt".to_string(),
title:"博客文章".to_string(),
collect: 20
};
let wechar :WeChatArticle = WeChatArticle
{
aothor:"matt".to_string(),
title:"微信公众号文章".to_string(),
timestamp:"1324111889".to_string()
};
notify(blog);
notify(wechar);
}
2. Generic form writing
//item是实现了Article这个Trait的类型,泛型写法对传入不用的类型阅读更友好
pub fn notify<T:Article>(item_1: T,item_2 : T)
{
print!("Article digest {} \n",item_1.digest());
}
3. Multiple Trait constraints
//item是实现了Article和Display两个Trait
pub fn notify<T:Article + Display>(item_1: T)
{
print!("Article digest {} \n",item_1.digest());
}
Use where clause to implement Trait constraints
pub fn notify<T,U>(item_1: T,item_2 : U)
where
T : Article + Display, //T要现了这两个Trait约束
U : Clone + Debug,
{
print!("Article digest {} \n",item_1.digest());
}
3. Implement Trait as the return type
//只能返回确定的同一种类型，返回不周类型会的代码会报错
pub fn notify( b : bool) -> impl Article
{
//这样会报错
// if(true)
// {
// Blog
// {
// aothor:"matt".to_string(),
// title:"博客文章".to_string(),
// collect: 20
// }
// }
// else
// {
// WeChatArticle
// {
// aothor:"matt".to_string(),
// title:"微信公众号文章".to_string(),
// timestamp:"1324111889".to_string()
// }
// }
WeChatArticle
{
aothor:"matt".to_string(),
title:"微信公众号文章".to_string(),
timestamp:"1324111889".to_string()
}
}