Comparisons
数据比较是Rust中的一个基础工具，通过该工具可以对变量或者对象做对比较。 Rust中的比较工具是通过trait实现的，实现之后重写对应的比较方法就可以实现对比。
PartialEq and Eq
struct Key {
id: u32,
metadata: Option<String>,
}
//实现PartialEq重写eq方法，通过id做比较
impl PartialEq for Key {
fn eq(&self, other: &Self) -> bool {
self.id == other.id
}
}
PartialOrd and Ord
PartialOrd在Rust中用于排序，并且可以实现<, <=, >=, and >四种类型的排序。
use std::cmp::Ordering;
#[derive(Eq, PartialEq)]
struct Citation {
author: String,
year: u32,
}
impl PartialOrd for Citation {
fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
match self.author.partial_cmp(&other.author) {
Some(Ordering::Equal) => self.year.partial_cmp(&other.year),
author_ord => author_ord,
}
}
}
impl Ord for Citation {
fn cmp(&self, other: &Self) -> Ordering {
todo!()
}
}
From and Into
类型转换是Rust中通过trait提供的类型转换工具，From和Into本质上都是做类型转换，主要的区别就是所属的trait不同。
fn main() {
let s = String::from("hello");
let addr = std::net::Ipv4Addr::from([127, 0, 0, 1]);
let one = i16::from(true);
let bigger = i32::from(123_i16);
println!("{s}, {addr}, {one}, {bigger}");
}
fn main() {
let s: String = "hello".into();
let addr: std::net::Ipv4Addr = [127, 0, 0, 1].into();
let one: i16 = true.into();
let bigger: i32 = 123_i16.into();
println!("{s}, {addr}, {one}, {bigger}");
}
//实现From的trait重写from
impl From for Citation {
fn from(value: T) -> Self {
todo!()
}
}
Casting
Casting也是类型转换，具体是通过as实现的转换。和From、Into的区别是From和Into是trait需要实现重写对应方法才可以实现，但是as是一个关键字直接使用即可。
fn main() {
let value: i64 = 1000;
println!("as u16: {}", value as u16);
println!("as i16: {}", value as i16);
println!("as u8: {}", value as u8);
}
但是使用as会容易出错，如果类型的确不一致，强行使用as会出现异常。
Read and Write
IO读和IO写。
Rust中的IO操作也是通过缓冲区实现的，类似Java。
Read
use std::io::{BufRead, BufReader, Read, Result};
fn count_lines<R: Read>(reader: R) -> usize {
let buf_reader = BufReader::new(reader);
buf_reader.lines().count()
}
fn main() -> Result<()> {
let slice: &[u8] = b"foo\nbar\nbaz\n";
println!("lines in slice: {}", count_lines(slice));
let file = std::fs::File::open(std::env::current_exe()?)?;
println!("lines in file: {}", count_lines(file));
Ok(())
}
Write
use std::io::{Result, Write};
fn log<W: Write>(writer: &mut W, msg: &str) -> Result<()> {
writer.write_all(msg.as_bytes())?;
writer.write_all("\n".as_bytes())
}
fn main() -> Result<()> {
let mut buffer = Vec::new();
log(&mut buffer, "Hello")?;
log(&mut buffer, "World")?;
println!("Logged: {:?}", buffer);
Ok(())
}
Closures
闭包
