From 20156d1ac93120510fbff22dc23a00fb009b6b3a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Grzegorz=20=C5=9Awirski?= <grzegorz@swirski.name>
Date: Thu, 17 Apr 2025 22:11:46 +0200
Subject: [PATCH] Cow without std

---
 miden-crypto/src/merkle/sparse_path.rs | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/miden-crypto/src/merkle/sparse_path.rs b/miden-crypto/src/merkle/sparse_path.rs
index c8f3b34..c8f9971 100644
--- a/miden-crypto/src/merkle/sparse_path.rs
+++ b/miden-crypto/src/merkle/sparse_path.rs
@@ -2,8 +2,8 @@ use alloc::vec::Vec;
 use core::{
     iter::{self, FusedIterator},
     num::NonZero,
+    ops::Deref,
 };
-use std::borrow::Cow;
 
 use winter_utils::{Deserializable, DeserializationError, Serializable};
 
@@ -253,10 +253,26 @@ impl From<SparseMerklePath> for Vec<RpoDigest> {
 // ITERATORS
 // ================================================================================================
 
+enum Inner<'a, T> {
+    Owned(T),
+    Borrowed(&'a T),
+}
+
+impl<'a, T> Deref for Inner<'a, T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        match *self {
+            Self::Borrowed(borrowed) => borrowed,
+            Self::Owned(ref owned) => &owned,
+        }
+    }
+}
+
 /// Iterator for [`SparseMerklePath`].
 pub struct SparseMerklePathIter<'p> {
     /// The "inner" value we're iterating over.
-    path: Cow<'p, SparseMerklePath>,
+    path: Inner<'p, SparseMerklePath>,
 
     /// The depth a `next()` call will get. `next_depth == 0` indicates that the iterator has been
     /// exhausted.
@@ -304,7 +320,7 @@ impl IntoIterator for SparseMerklePath {
     fn into_iter(self) -> SparseMerklePathIter<'static> {
         let tree_depth = self.depth();
         SparseMerklePathIter {
-            path: Cow::Owned(self),
+            path: Inner::Owned(self),
             next_depth: tree_depth,
         }
     }
@@ -317,7 +333,7 @@ impl<'p> IntoIterator for &'p SparseMerklePath {
     fn into_iter(self) -> SparseMerklePathIter<'p> {
         let tree_depth = self.depth();
         SparseMerklePathIter {
-            path: Cow::Borrowed(self),
+            path: Inner::Borrowed(self),
             next_depth: tree_depth,
         }
     }