macro_rules! try { ($expr:expr $(,)?) => { ... }; }
👎Deprecated since 1.39.0: use the
?
operator insteadExpand description
Unwraps a result or propagates its error.
The ?
operator was added to replace try!
and should be used instead. Furthermore, try
is a reserved word
in Rust 2018, so if you must use it, you will need to use the
raw-identifier syntax: r#try
.
try!
matches the given Result
. In case of the Ok
variant, the
expression has the value of the wrapped value.
In case of the Err
variant, it retrieves the inner error. try!
then
performs conversion using From
. This provides automatic conversion
between specialized errors and more general ones. The resulting
error is then immediately returned.
Because of the early return, try!
can only be used in functions that
return Result
.
§Examples
use std::io;
use std::fs::File;
use std::io::prelude::*;
enum MyError {
FileWriteError
}
impl From<io::Error> for MyError {
fn from(e: io::Error) -> MyError {
MyError::FileWriteError
}
}
// The preferred method of quick returning Errors
fn write_to_file_question() -> Result<(), MyError> {
let mut file = File::create("my_best_friends.txt")?;
file.write_all(b"This is a list of my best friends.")?;
Ok(())
}
// The previous method of quick returning Errors
fn write_to_file_using_try() -> Result<(), MyError> {
let mut file = r#try!(File::create("my_best_friends.txt"));
r#try!(file.write_all(b"This is a list of my best friends."));
Ok(())
}
// This is equivalent to:
fn write_to_file_using_match() -> Result<(), MyError> {
let mut file = r#try!(File::create("my_best_friends.txt"));
match file.write_all(b"This is a list of my best friends.") {
Ok(v) => v,
Err(e) => return Err(From::from(e)),
}
Ok(())
}
Run