Я пытаюсь добавить более краткую версию failure
ящика .with_context(|e| format!("foo: {}", e))
в мой код. Вот так детская площадка :
use failure::{Context, Fail, ResultExt}; // 0.1.5
/// Extension methods for failure `Result`.
pub trait ResultContext<T, E> {
/// Wraps the error type in a context type generated by looking at the
/// error value. This is very similar to `with_context` but much more
/// concise.
fn ctx(self, s: &str) -> Result<T, Context<String>>;
}
impl<T, E> ResultContext<T, E> for Result<T, E>
where
E: Fail,
{
fn ctx(self, s: &str) -> Result<T, Context<String>> {
self.map_err(|failure| {
let context = format!("{}: {}", s, failure);
failure.context(context)
})
}
}
pub fn foo() -> Result<i32, failure::Error> {
Ok(5i32)
}
pub fn main() -> Result<(), failure::Error> {
// This works.
let _ = foo().with_context(|_| "foo".to_string())?;
// This doesn't.
foo().ctx("foo")?
}
Я получаю следующую ошибку:
error[E0599]: no method named `ctx` found for type `std::result::Result<i32, failure::error::Error>` in the current scope
--> src/main.rs:31:11
|
31 | foo().ctx("foo")?
| ^^^
|
= note: the method `ctx` exists but the following trait bounds were not satisfied:
`std::result::Result<i32, failure::error::Error> : ResultContext<_, _>`
= help: items from traits can only be used if the trait is implemented and in scope
= note: the following trait defines an item `ctx`, perhaps you need to implement it:
candidate #1: `ResultContext`
Я не могу понять, почему. Я более или менее скопировал существующий код with_context
.