add slice_ext

libs/riff/src/lib.rs

@@ -6,6 +6,7 @@ mod bitmask_operations;
 mod change_min_max;
 mod numeric_traits;
 mod pop_if;
+mod slice_ext;
 
 pub use binary_search::BinarySearch;
 pub use bitmask_iterators::bitmask_combinations;
@@ -14,3 +15,4 @@ pub use bitmask_operations::i2powm1;
 pub use change_min_max::ChangeMinMax;
 pub use numeric_traits::Unsigned;
 pub use pop_if::PopIf;
+pub use slice_ext::SliceExt;

libs/riff/src/slice_ext.rs

@@ -0,0 +1,44 @@
+/// A trait for slices.
+pub trait SliceExt {
+    type Item;
+    /// Groups adjacent elements by a predicate.
+    /// (Rust 1.77.0)
+    fn chunk_by<F>(&self, f: F) -> SliceChunkBy<'_, Self::Item, F>
+    where
+        F: FnMut(&Self::Item, &Self::Item) -> bool;
+}
+impl<T> SliceExt for [T] {
+    type Item = T;
+
+    fn chunk_by<F>(&self, f: F) -> SliceChunkBy<'_, Self::Item, F>
+    where
+        F: FnMut(&Self::Item, &Self::Item) -> bool,
+    {
+        SliceChunkBy { a: self, f }
+    }
+}
+
+pub struct SliceChunkBy<'a, T, F> {
+    a: &'a [T],
+    f: F,
+}
+impl<'a, T, F> Iterator for SliceChunkBy<'a, T, F>
+where
+    F: FnMut(&T, &T) -> bool,
+{
+    type Item = &'a [T];
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let Self { a, f } = self;
+        if a.is_empty() {
+            return None;
+        }
+        let mut end = 1;
+        while end < a.len() && f(&a[end - 1], &a[end]) {
+            end += 1;
+        }
+        let (prefix, rest) = a.split_at(end);
+        self.a = rest;
+        Some(prefix)
+    }
+}