16.6 Result as an alias
What if the specific Result type is reused many many times? Then quickly it becomes tedious
to write out the full type name. Instead, a generic alias for the specific Result may be
defined.
use std::num::ParseIntError;
use std::result;
// A generic alias for any `Result` with this specific `Err` type.
type Result<T> = result::Result<T, ParseIntError>;
// Use the alias defined above referring to our specific `Result` type.
fn double_number(number_str: &str) -> Result<i32> {
number_str.parse::<i32>().map(|n| 2 * n)
}
// Again, the alias saved us from defining it again.
fn print(result: Result<i32>) {
match result {
Ok(n) => println!("n is {}", n),
Err(e) => println!("Error: {}", e),
}
}
fn main() {
print(double_number("10"));
print(double_number("t"));
}
This is particularly helpful at a module level because all errors found in a specific module
may have the same Err type; a single alias succinctly defines all module Results. This
is so useful that the std library even supplies one: io::Result which refers to IO errors.
See also:
Result and io::Result