mirror of
https://github.com/rust-lang/rustlings
synced 2024-11-08 19:10:25 +00:00
66 lines
2.3 KiB
Rust
66 lines
2.3 KiB
Rust
// errors5.rs
|
|
|
|
// This program uses an altered version of the code from errors4.
|
|
|
|
// This exercise 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, which, given
|
|
// Rust's usual standards for runtime safety, should strike you as somewhat lenient!
|
|
|
|
// 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.
|
|
|
|
// What can we use to describe both errors? In other words, is there a trait which both errors implement?
|
|
|
|
// Execute `rustlings hint errors5` or use the `hint` watch subcommand for a hint.
|
|
|
|
// I AM NOT DONE
|
|
|
|
use std::error;
|
|
use std::fmt;
|
|
use std::num::ParseIntError;
|
|
|
|
// TODO: update the return type of `main()` to make this compile.
|
|
fn main() -> Result<(), Box<dyn ???>> {
|
|
let pretend_user_input = "42";
|
|
let x: i64 = pretend_user_input.parse()?;
|
|
println!("output={:?}", PositiveNonzeroInteger::new(x)?);
|
|
Ok(())
|
|
}
|
|
|
|
// Don't change anything below this line.
|
|
|
|
#[derive(PartialEq, Debug)]
|
|
struct PositiveNonzeroInteger(u64);
|
|
|
|
#[derive(PartialEq, Debug)]
|
|
enum CreationError {
|
|
Negative,
|
|
Zero,
|
|
}
|
|
|
|
impl PositiveNonzeroInteger {
|
|
fn new(value: i64) -> Result<PositiveNonzeroInteger, CreationError> {
|
|
match value {
|
|
x if x < 0 => Err(CreationError::Negative),
|
|
x if x == 0 => Err(CreationError::Zero),
|
|
x => Ok(PositiveNonzeroInteger(x as u64))
|
|
}
|
|
}
|
|
}
|
|
|
|
// This is required so that `CreationError` can implement `error::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::Error for CreationError {}
|