how.rs/src/explain.rs

use crate::{How, IntoContext, IntoResultHow};

crate::seal!(pub(crate) private::Sealed);

pub trait Explain: Sealed {
    type Output;

    #[must_use]
    fn context(self, context: impl IntoContext) -> Self::Output;
}

impl<T, E> Sealed for Result<T, E> where Result<T, E>: IntoResultHow {}
impl<T> Sealed for Option<T> where Option<T>: IntoResultHow {}

impl<T, E> Explain for Result<T, E>
where
    Result<T, E>: IntoResultHow,
{
    type Output = Result<<Self as IntoResultHow>::T, How>;

    #[inline(always)]
    #[track_caller]
    fn context(self, context: impl IntoContext) -> Self::Output {
        self.into_result_how().map_err(#[inline(never)] move |e| e.context(context))
    }
}

impl<T> Explain for Option<T> {
    type Output = Result<T, How>;

    #[inline(always)]
    #[track_caller]
    fn context(self, context: impl IntoContext) -> Self::Output {
        // TODO: maybe add a feature for the extra "Option::None" context
        match self {
            Some(t) => Ok(t),
            None => Err(How::new(context))
        }
        //self.into_result_how().map_err(#[inline(never)] move |e| e.context(context))
    }
}