1 files changed, 42 insertions, 0 deletions
diff --git a/vendor/im-rc/src/iter.rs b/vendor/im-rc/src/iter.rs
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+++ b/vendor/im-rc/src/iter.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/.
+
+//! Iterators over immutable data.
+
+/// Create an iterator of values using a function to update an owned state
+/// value.
+///
+/// The function is called with the current state as its argument, and should
+/// return an [`Option`][std::option::Option] of a tuple of the next value to
+/// yield from the iterator and the updated state. If the function returns
+/// [`None`][std::option::Option::None], the iterator ends.
+///
+/// # Examples
+/// ```
+/// # #[macro_use] extern crate im_rc as im;
+/// # use im::iter::unfold;
+/// # use im::vector::Vector;
+/// # use std::iter::FromIterator;
+/// // Create an infinite stream of numbers, starting at 0.
+/// let mut it = unfold(0, |i| Some((i, i + 1)));
+///
+/// // Make a list out of its first five elements.
+/// let numbers = Vector::from_iter(it.take(5));
+/// assert_eq!(numbers, vector![0, 1, 2, 3, 4]);
+/// ```
+///
+/// [std::option::Option]: https://doc.rust-lang.org/std/option/enum.Option.html
+/// [std::option::Option::None]: https://doc.rust-lang.org/std/option/enum.Option.html#variant.None
+pub fn unfold<F, S, A>(value: S, f: F) -> impl Iterator<Item = A>
+where
+    F: Fn(S) -> Option<(A, S)>,
+{
+    let mut value = Some(value);
+    std::iter::from_fn(move || {
+        f(value.take().unwrap()).map(|(next, state)| {
+            value = Some(state);
+            next
+        })
+    })
+}