|
|
|
|
|
// errors5.rs
|
|
|
|
|
|
|
|
|
|
|
|
// 这个程序使用练习 errors4 代码的完整版。
|
|
|
|
|
|
// 它现在不能编译! 为什么呢？
|
|
|
|
|
|
// 执行 `rustlings hint errors5` 获取提示！
|
|
|
|
|
|
|
|
|
|
|
|
// I AM NOT DONE
|
|
|
|
|
|
|
|
|
|
|
|
use std::error;
|
|
|
|
|
|
use std::fmt;
|
|
|
|
|
|
use std::num::ParseIntError;
|
|
|
|
|
|
|
|
|
|
|
|
// TODO：修改 `main()` 的返回类型，以使其通过编译。
|
|
|
|
|
|
fn main() -> Result<(), ParseIntError> {
|
|
|
|
|
|
let pretend_user_input = "42";
|
|
|
|
|
|
let x: i64 = pretend_user_input.parse()?;
|
|
|
|
|
|
println!("output={:?}", PositiveNonzeroInteger::new(x)?);
|
|
|
|
|
|
Ok(())
|
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
|
|
// 不要更改此行以下的任何内容。
|
|
|
|
|
|
|
|
|
|
|
|
#[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))
|
|
|
|
|
|
}
|
|
|
|
|
|
}
|
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
|
|
// 以下是必要的，以便 `CreationError` 能够实现 `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 {}
|
