为ParseIntError实现From特性

Question

When using the try! macro, it uses the From trait to transform an error into the desired error.

I would like to transform some errors into my own type. This goes great for eg io::Error, but I can't get it to work for an error type from core.

use std::io;

pub struct ParserError {
    pub message: String,
}

impl From<io::Error> for ParserError {
    fn from(e: io::Error) -> ParserError {
        ParserError{message: format!("Generic IO error: {}", e.description())}
    }
}

This works well for doing try! on anything io. But now for parsing:

fn parse_string(s: &str) -> Result<u64, ParserError> {
    let i = try!(s.parse::<u64>());
    return Ok(i);
}

My error says:

error: the trait core::convert::From<parser::ParserError> is not implemented for the type `core::num::ParseIntError

I tried to implement this From:

impl From<core::num::ParseIntError> for ParserError {
    fn from(_: core::num::ParseIntError) -> ParserError {
        ParserError{message: "Invalid data type".to_string()}
    }
}

But I can't get core imported. How to do this?

Answer 1

The modules from core are reexported by std . You can fix your error by just replacing core by std in your code:

impl From<std::num::ParseIntError> for ParserError {
    fn from(_: std::num::ParseIntError) -> ParserError {
        ParserError{message: "Invalid data type".to_string()}
    }
}