16.7 Options with Results
The previous examples have always been very convenient; a Result interacts with the same
Results and an Option with the same Option. Sometimes it is not this easy though;
Options and Results may have to interact or even Result<T, Error1> with
Result<T, Error2>.
Here is an example where one returns an Option and the other returns an Result. Aside
from messy errors provided by unwrap, this looks reasonable:
// The first attempt conveniently uses `unwrap` with the aforementioned
// bad errors it results in.
fn double_first(vec: Vec<&str>) -> i32 {
// What if the vector is empty?
let first = vec.first().unwrap();
// What if the element doesn't parse to a number?
2 * first.parse::<i32>().unwrap()
}
fn main() {
let numbers = vec!["93", "18"];
let empty = vec![];
let strings = vec!["tofu", "93", "18"];
println!("The first doubled is {}", double_first(numbers));
println!("The first doubled is {}", double_first(empty));
// ^ Comment out this line to see the second error.
println!("The first doubled is {}", double_first(strings));
}
See also:
Result and io::Result