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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]);
+}