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rustlings/solutions/13_error_handling/errors5.rs
2024-06-26 18:21:19 +02:00

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1.8 KiB
Rust

// This exercise is an altered version of the `errors4` exercise. It uses some
// concepts that we won't get to until later in the course, like `Box` and the
// `From` trait. It's not important to understand them in detail right now, but
// you can read ahead if you like. For now, think of the `Box<dyn ???>` type as
// an "I want anything that does ???" type.
//
// In short, this particular use case for boxes is for when you want to own a
// value and you care only that it is a type which implements a particular
// trait. To do so, The `Box` is declared as of type `Box<dyn Trait>` where
// `Trait` is the trait the compiler looks for on any value used in that
// context. For this exercise, that context is the potential errors which
// can be returned in a `Result`.
use std::error::Error;
use std::fmt;
#[derive(PartialEq, Debug)]
enum CreationError {
Negative,
Zero,
}
// This is required so that `CreationError` can implement `Error`.
impl fmt::Display for CreationError {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
let description = match *self {
CreationError::Negative => "number is negative",
CreationError::Zero => "number is zero",
};
f.write_str(description)
}
}
impl Error for CreationError {}
#[derive(PartialEq, Debug)]
struct PositiveNonzeroInteger(u64);
impl PositiveNonzeroInteger {
fn new(value: i64) -> Result<PositiveNonzeroInteger, CreationError> {
match value {
x if x < 0 => Err(CreationError::Negative),
0 => Err(CreationError::Zero),
x => Ok(PositiveNonzeroInteger(x as u64)),
}
}
}
fn main() -> Result<(), Box<dyn Error>> {
let pretend_user_input = "42";
let x: i64 = pretend_user_input.parse()?;
println!("output={:?}", PositiveNonzeroInteger::new(x)?);
Ok(())
}