resiter/
onerr.rs

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//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.
//

#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
pub struct OnErr<I, O, E, F>(I, F)
where
    I: Iterator<Item = Result<O, E>>,
    F: FnMut(&E);

/// Extension trait for `Iterator<Item = Result<T, E>>` to do something on `Err(_)`
pub trait OnErrDo<I, O, E, F>
where
    I: Iterator<Item = Result<O, E>>,
    F: FnMut(&E),
{
    /// Apply a sideffect on each `Err`
    ///
    /// ```
    /// use resiter::onerr::OnErrDo;
    /// use std::str::FromStr;
    ///
    /// let mut errs = Vec::<::std::num::ParseIntError>::new();
    /// let _: Vec<Result<usize, ::std::num::ParseIntError>> = ["1", "2", "a", "b", "5"]
    ///     .iter()
    ///     .map(|e| usize::from_str(e))
    ///     .on_err(|e| {
    ///         errs.push(e.to_owned())
    ///     })
    ///     .collect();
    ///
    /// assert_eq!(errs.len(), 2);
    /// ```
    fn on_err(self, _: F) -> OnErr<I, O, E, F>;
}

impl<I, O, E, F> OnErrDo<I, O, E, F> for I
where
    I: Iterator<Item = Result<O, E>>,
    F: FnMut(&E),
{
    #[inline]
    fn on_err(self, f: F) -> OnErr<I, O, E, F> {
        OnErr(self, f)
    }
}

impl<I, O, E, F> Iterator for OnErr<I, O, E, F>
where
    I: Iterator<Item = Result<O, E>>,
    F: FnMut(&E),
{
    type Item = Result<O, E>;

    fn next(&mut self) -> Option<Self::Item> {
        self.0.next().map(|r| {
            r.map_err(|e| {
                (self.1)(&e);
                e
            })
        })
    }
}