mirror of
https://github.com/notohh/rustlings.git
synced 2024-11-24 14:37:32 -05:00
54 lines
1.8 KiB
Rust
54 lines
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(())
|
|
}
|