我写了下面的代码解析字符串来得到它编码的整数,并检查使用match
错误。如果我得到一个Err(e)
我想打印出错误e
,并返回默认值。
return match t.parse::<usize>() {
Ok(n) => n,
Err(e) => {
println!("Couldn't parse the value for gateway_threads {}", e);
// Return two as a default value
return 2;
},
};
然而,代码编译失败,因为它预计键入()
却得到了一个整数:
error[E0308]: mismatched types
--> src/main.rs:37:32
|
37 | return 2;
| ^ expected (), found integral variable
|
= note: expected type `()`
found type `{integer}
如果我删除默认值的回报,我得到的错误expected usize but got `()`
:
error[E0308]: match arms have incompatible types
--> src/main.rs:33:24
|
33 | return match t.parse::<usize>() {
| ________________________^
34 | | Ok(n) => n,
35 | | Err(e) => {
36 | | println!("Couldn't parse the value for gateway_threads {}", e); //TODO: Log this
37 | | //return 2;
38 | | },
39 | | };
| |_________________^ expected usize, found ()
|
= note: expected type `usize`
found type `()`
note: match arm with an incompatible type
--> src/main.rs:35:31
|
35 | Err(e) => {
| _______________________________^
36 | | println!("Couldn't parse the value for gateway_threads {}", e); //TODO: Log this
37 | | //return 2;
38 | | },
| |_____________________^
完整的代码(我解析INI配置文件让我的一些值):
extern crate threadpool;
extern crate ini;
use std::net::{TcpListener, TcpStream};
use std::io::Read;
use std::process;
use threadpool::ThreadPool;
use ini::Ini;
fn main() {
let mut amount_workers: usize;
let mut network_listen = String::with_capacity(21);
//Load INI
{
let conf: Ini = match Ini::load_from_file("/etc/iotcloud/conf.ini") {
Ok(t) => t,
Err(e) => {
println!("Error load ini file {}", e);
process::exit(0);
},
};
let section = match conf.section(Some("network".to_owned())) {
Some(t) => t,
None => {
println!("Couldn't find the network ");
process::exit(0);
},
};
//amount_workers = section.get("gateway_threads").unwrap().parse().unwrap();
amount_workers = match section.get("gateway_threads") {
Some(t) => {
return match t.parse::<usize>() {
Ok(n) => n,
Err(e) => {
println!("Couldn't parse the value for gateway_threads {}", e);
// Return two as a default value
return 2; //ERROR HERE;
},
};
},
None => 2, // Return two as a default value
};
let ip = section.get("bind_ip").unwrap();
let port = section.get("bind_port").unwrap();
network_listen.push_str(ip);
network_listen.push_str(":");
network_listen.push_str(port);
}
}
是什么原因导致这个错误?
更改
amount_workers = match section.get("gateway_threads") {
Some(t) => {
return match t.parse::<usize>() {
Ok(n) => n,
Err(e) => {
println!("Couldn't parse the value for gateway_threads {}", e); //TODO: Log this
return 2; //ERROR HERE; //Default value is set to 2
}
};
}
None => 2, //Default value is set to 2
};
至
amount_workers = match section.get("gateway_threads") {
Some(t) => {
match t.parse::<usize>() { // No return
Ok(n) => n,
Err(e) => {
println!("Couldn't parse the value for gateway_threads {}", e); //TODO: Log this
2 // No semicolon, no return
}
} // No semicolon
}
None => 2, //Default value is set to 2
};
不是终止与;
声明是你如何在锈返回值。当你想要一个全功能的最后一行,这就是为什么称它为一个“早归”之前返回值的return
使用关键字。
你会发现担心生锈如何处理表达式here更多信息。