用Box< error :: Error>装箱后如何处理不同的错误类型? [英] How to handle different error types after boxing them with Box<error::Error>?
问题描述
In my try to better handle errors and prevent repeating tio much code, I am implementing the ?, operator returning Result<bool, Box<error::Error>> so that I could just match the error once instead of multiple times.
我使用多个 match es更改了以下代码:
I changed the following code using multiple matches:
fn example(pool: mysql::Pool) {
let now = match SystemTime::now().duration_since(SystemTime::UNIX_EPOCH) {
Ok(n) => n.as_secs(),
Err(_) => panic!("SystemTime before UNIX EPOCH!"),
};
// create table
match pool.prep_exec("CREATE TABLE IF NOT EXISTS dbpulse_rw (id INT NOT NULL, t INT(11) NOT NULL, PRIMARY KEY(id))", ()) {
Ok(_) => (),
Err(e) => {
eprintln!("{}", e);
return;
}
}
// write into table
let mut stmt = match pool
.prepare("INSERT INTO dbpulse_rw (id, t) VALUES (1, ?) ON DUPLICATE KEY UPDATE t=?")
{
Ok(stmt) => stmt,
Err(e) => {
eprintln!("{}", e);
return;
}
};
match stmt.execute((now, now)) {
Ok(_) => (),
Err(mysql::Error::IoError(e)) => {
eprintln!("IoError: {}", e);
// send alert
return;
}
Err(e) => {
eprintln!("{}", e);
return;
}
}
let items = match pool.prep_exec("SELECT t FROM dbpulse_rw WHERE id=1", ()) {
Ok(n) => n,
Err(mysql::Error::IoError(e)) => {
eprintln!("IoError: {}", e);
//send_alert
return;
}
Err(e) => {
eprintln!("{}", e);
return;
}
};
for row in items {
let pool = pool.clone();
let rs = mysql::from_row::<u64>(row.unwrap());
if now != rs {
// send alert
}
assert_eq!(now, rs);
}
}
要使用?运算符，请执行以下操作:
To use the ? operator:
fn example(pool: mysql::Pool) -> Result<bool, Box<error::Error>> {
let n = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH)?;
let now = n.as_secs();
// create table
pool.prep_exec("CREATE TABLE IF NOT EXISTS dbpulse_rw (id INT NOT NULL, t INT(11) NOT NULL, PRIMARY KEY(id))", ())?;
// write into table
let mut stmt = pool
.prepare("INSERT INTO dbpulse_rw (id, t) VALUES (1, ?) ON DUPLICATE KEY UPDATE t=?")?;
stmt.execute((now, now))?;
pool.prep_exec("SELECT t FROM dbpulse_rw WHERE id=1", ())
.map(|items| {
for row in items {
match row {
Ok(row) => {
let rs = mysql::from_row::<u64>(row);
if now != rs {
// send alert
}
}
Err(e) => println!("{}", e),
}
}
})?;
Ok(true)
}
我现在想做的是根据错误(超时或查询错误或其他错误类型)进行 match 匹配.我正在这样创建MySQL池:
What I would like to do now is to match based on the error, either a timeout or a query error, or other error type. I am creating the MySQL pool like this:
let mut opts = mysql::OptsBuilder::from_opts(dsn);
opts.stmt_cache_size(0);
opts.read_timeout(Some(Duration::new(3, 0)));
opts.write_timeout(Some(Duration::new(3, 0)));
let pool = mysql::Pool::new_manual(1, 5, opts).expect("Could not connect to MySQL");
如果查询花费了3秒钟以上的时间，它将返回 mysql :: Error :: IoError ，我想在其他可能的错误之间进行区分，到目前为止，我已经尝试过:
If a query takes more than 3 seconds it will return a mysql::Error::IoError the one I would like to distinguish between other possible errors, so far I have tried:
fun run_example() {
match example() {
Ok(_) => (),
Err(mysql::Error::IoError(e)) => {
eprintln!("IoError: {}", e);
// send alert
return;
}
Err(e) => {
eprintln!("{}", e);
return;
}
}
}
但是我收到类型不匹配的错误:
But I am getting a mismatched types error:
expected struct `std::boxed::Box`, found enum `mysql::error::Error`
有关如何实施此操作的任何提示或更好的主意?
Any tips or better ideas about how to implement this?
推荐答案
使用特质会丢失具体的类型信息.某些错误包装箱可能会对您有所帮助，但这意味着将特征转换为具体类型，因此在运行时可能会失败.
You lose the concrete type information by using a trait. Some error crate could help you, but this implies casting a trait to a concrete type and so could fail at runtime.
我建议您创建一个 MyError 类型，并列出您的函数可能产生的所有潜在错误.然后，您可以很好，快速地匹配实际错误.例如，使用 SNAFU
I advise you to create a type MyError and list all potential errors that your function could produce. You can then match the real error nicely and fast. For example, use SNAFU
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