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- // imag - the personal information management suite for the commandline
- // Copyright (C) 2015, 2016 Matthias Beyer <mail@beyermatthias.de> and contributors
- //
- // This library is free software; you can redistribute it and/or
- // modify it under the terms of the GNU Lesser General Public
- // License as published by the Free Software Foundation; version
- // 2.1 of the License.
- //
- // This library is distributed in the hope that it will be useful,
- // but WITHOUT ANY WARRANTY; without even the implied warranty of
- // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- // Lesser General Public License for more details.
- //
- // You should have received a copy of the GNU Lesser General Public
- // License along with this library; if not, write to the Free Software
- // Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
- //
- /// Folds its contents to a result.
- pub trait FoldResult: Sized {
- type Item;
- /// Apply a `FnMut(Self::Item) -> Result<R, E>` to each item. If each
- /// application returns an `Ok(_)`, return `Ok(())`, indicating success.
- /// Otherwise return the first error.
- ///
- /// The return type of this function only indicates success with the
- /// `Ok(())` idiom. To retrieve the values of your application, include an
- /// accumulator in `func`. This is the intended reason for the permissive
- /// `FnMut` type.
- fn fold_result<R, E, F>(self, func: F) -> Result<(), E>
- where F: FnMut(Self::Item) -> Result<R, E>;
- }
- impl<X, I: Iterator<Item = X>> FoldResult for I {
- type Item = X;
- fn fold_result<R, E, F>(self, mut func: F) -> Result<(), E>
- where F: FnMut(Self::Item) -> Result<R, E>
- {
- for item in self {
- try!(func(item));
- }
- Ok(())
- }
- }
- #[test]
- fn test_fold_result_success() {
- let v = vec![1, 2, 3];
- let mut accum = vec![];
- let result: Result<(), &str> = v.iter().fold_result(|item| {
- accum.push(*item * 2);
- Ok(*item)
- });
- assert_eq!(result, Ok(()));
- assert_eq!(accum, vec![2, 4, 6]);
- }
- #[test]
- fn test_fold_result_failure() {
- let v: Vec<usize> = vec![1, 2, 3];
- let mut accum: Vec<usize> = vec![];
- let result: Result<(), &str> = v.iter().fold_result(|item| if *item == 2 {
- Err("failure")
- } else {
- accum.push(*item * 2);
- Ok(*item)
- });
- assert_eq!(result, Err("failure"));
- assert_eq!(accum, vec![2]);
- }
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