我正在使用 std::time::SystemTime .我的目标是创建一个结构，其中包含一个名为 timestamp 的字段，并以秒为单位存储时间。
我看到这个例子可以正常工作:
use std::time::SystemTime;
match SystemTime::now().duration_since(SystemTime::UNIX_EPOCH) {
Ok(n) => println!("1970-01-01 00:00:00 UTC was {} seconds ago!", n.as_secs()),
Err(_) => panic!("SystemTime before UNIX EPOCH!"),
}
当我尝试此代码时出现错误:
use std::time::SystemTime;
let n = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH);
println!("{}", n.as_secs());
error[E0599]: no method named `as_secs` found for enum `std::result::Result<std::time::Duration, std::time::SystemTimeError>` in the current scope
--> src/main.rs:5:22
|
5 | println!("{}", n.as_secs());
| ^^^^^^^ method not found in `std::result::Result<std::time::Duration, std::time::SystemTimeError>`
我做错了什么？
读取错误:
no method named `...` found for type `Result<...>`
所以，我们看Result :
Result is a type that represents either success (Ok) or faliure (Err)
See the std::result module for documentation details.
所以，我们知道 SystemTime::duration_since(&self, _)返回一个 Result，这意味着它可能失败了。阅读文档:
Returns an Err if earlier is later than self, and the error contains how far from self the time is.
所以，我们只需要 unwrap , expect ，或匹配它以获得错误的可能性:
use std::time::SystemTime;
// Unwrapping
let n = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH)
.unwrap(); // Will panic if it is not `Ok`.
// Expecting
let n = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH)
.expect("Invalid time comparison"); // Will panic with error message
// if it is not `Ok`.
// Matching
let n = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH);
match n {
Ok(x) => { /* Use x */ },
Err(e) => { /* Process Error e */ },
}
// Fallibly Destructuring:
let n = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH);
if let Ok(x) = n {
/* Use x */
} else {
/* There was an error. */
}