16.3.2 aliases for Result
How about when we want to reuse a specific Result type many times?
Recall that Rust allows us to create aliases. Conveniently,
we can define one for the specific Result in question.
At a module level, creating aliases can be particularly helpful. Errors
found in a specific module often have the same Err type, so a single alias
can succinctly define all associated Results. This is so useful that the std library even supplies one: io::Result!
Here's a quick example to show off the syntax:
use std::num::ParseIntError;
use std::result;
// Define a generic alias for a `Result` with the error type `ParseIntError`.
type AliasedResult<T> = result::Result<T, ParseIntError>;
// Use the above alias to refer to our specific `Result` type.
fn double_number(number_str: &str) -> AliasedResult<i32> {
number_str.parse::<i32>().map(|n| 2 * n)
}
// Here, the alias again allows us to save some space.
fn print(result: AliasedResult<i32>) {
match result {
Ok(n) => println!("n is {}", n),
Err(e) => println!("Error: {}", e),
}
}
fn main() {
print(double_number("10"));
print(double_number("t"));
}See also:
Result and io::Result