1 files changed, 95 insertions, 0 deletions
diff --git a/third_party/rust/generic-array/src/functional.rs b/third_party/rust/generic-array/src/functional.rs
new file mode 100644
index 0000000000..2ddcc5c4c4
--- /dev/null
+++ b/third_party/rust/generic-array/src/functional.rs
@@ -0,0 +1,95 @@
+//! Functional programming with generic sequences
+//!
+//! Please see `tests/generics.rs` for examples of how to best use these in your generic functions.
+
+use super::ArrayLength;
+use core::iter::FromIterator;
+
+use crate::sequence::*;
+
+/// Defines the relationship between one generic sequence and another,
+/// for operations such as `map` and `zip`.
+pub unsafe trait MappedGenericSequence<T, U>: GenericSequence<T>
+where
+    Self::Length: ArrayLength<U>,
+{
+    /// Mapped sequence type
+    type Mapped: GenericSequence<U, Length = Self::Length>;
+}
+
+unsafe impl<'a, T, U, S: MappedGenericSequence<T, U>> MappedGenericSequence<T, U> for &'a S
+where
+    &'a S: GenericSequence<T>,
+    S: GenericSequence<T, Length = <&'a S as GenericSequence<T>>::Length>,
+    <S as GenericSequence<T>>::Length: ArrayLength<U>,
+{
+    type Mapped = <S as MappedGenericSequence<T, U>>::Mapped;
+}
+
+unsafe impl<'a, T, U, S: MappedGenericSequence<T, U>> MappedGenericSequence<T, U> for &'a mut S
+where
+    &'a mut S: GenericSequence<T>,
+    S: GenericSequence<T, Length = <&'a mut S as GenericSequence<T>>::Length>,
+    <S as GenericSequence<T>>::Length: ArrayLength<U>,
+{
+    type Mapped = <S as MappedGenericSequence<T, U>>::Mapped;
+}
+
+/// Accessor type for a mapped generic sequence
+pub type MappedSequence<S, T, U> =
+    <<S as MappedGenericSequence<T, U>>::Mapped as GenericSequence<U>>::Sequence;
+
+/// Defines functional programming methods for generic sequences
+pub unsafe trait FunctionalSequence<T>: GenericSequence<T> {
+    /// Maps a `GenericSequence` to another `GenericSequence`.
+    ///
+    /// If the mapping function panics, any already initialized elements in the new sequence
+    /// will be dropped, AND any unused elements in the source sequence will also be dropped.
+    fn map<U, F>(self, f: F) -> MappedSequence<Self, T, U>
+    where
+        Self: MappedGenericSequence<T, U>,
+        Self::Length: ArrayLength<U>,
+        F: FnMut(Self::Item) -> U,
+    {
+        FromIterator::from_iter(self.into_iter().map(f))
+    }
+
+    /// Combines two `GenericSequence` instances and iterates through both of them,
+    /// initializing a new `GenericSequence` with the result of the zipped mapping function.
+    ///
+    /// If the mapping function panics, any already initialized elements in the new sequence
+    /// will be dropped, AND any unused elements in the source sequences will also be dropped.
+    #[inline]
+    fn zip<B, Rhs, U, F>(self, rhs: Rhs, f: F) -> MappedSequence<Self, T, U>
+    where
+        Self: MappedGenericSequence<T, U>,
+        Rhs: MappedGenericSequence<B, U, Mapped = MappedSequence<Self, T, U>>,
+        Self::Length: ArrayLength<B> + ArrayLength<U>,
+        Rhs: GenericSequence<B, Length = Self::Length>,
+        F: FnMut(Self::Item, Rhs::Item) -> U,
+    {
+        rhs.inverted_zip2(self, f)
+    }
+
+    /// Folds (or reduces) a sequence of data into a single value.
+    ///
+    /// If the fold function panics, any unused elements will be dropped.
+    fn fold<U, F>(self, init: U, f: F) -> U
+    where
+        F: FnMut(U, Self::Item) -> U,
+    {
+        self.into_iter().fold(init, f)
+    }
+}
+
+unsafe impl<'a, T, S: GenericSequence<T>> FunctionalSequence<T> for &'a S
+where
+    &'a S: GenericSequence<T>,
+{
+}
+
+unsafe impl<'a, T, S: GenericSequence<T>> FunctionalSequence<T> for &'a mut S
+where
+    &'a mut S: GenericSequence<T>,
+{
+}