use std::convert::TryFrom;

#[derive(Debug)]
struct Src {
    fld1: Option<String>,
}

#[derive(Debug)]
struct Dst {
    fld2: String,
}

#[derive(Debug)]
pub struct ConvertError<'a> {
    msg: &'a str,
}

impl<'a> TryFrom<'a Src> for Dst {
    type Error = ConvertError<'a>;

    fn try_from(src: Src) -> Result<Self, Self::Error> {
        let s = src
            .fld1
            .ok_or(ConvertError {
                msg: "damn",
            })
            .and_then(|val| Ok(val))?;
        Ok(Dst { fld2: s })
    }
}

fn main() {
    let src = Src { fld1: None };
    let src1 = Src {
        fld1: Some(String::from("ciao")),
    };
    println!("{:?}", Dst::try_from(src));
    println!("{:?}", Dst::try_from(src1));
}