Add default constructors to MmrPeaks and PartialMmr (#409)

CHANGELOG.md

@@ -1,5 +1,6 @@
 ## 0.15.0 (TBD)
 
+- Added default constructors to `MmrPeaks` and `PartialMmr` (#409).
 
 ## 0.14.0 (2025-03-15)
 

miden-crypto/src/merkle/mmr/partial.rs

@@ -70,6 +70,18 @@ pub struct PartialMmr {
     pub(crate) track_latest: bool,
 }
 
+impl Default for PartialMmr {
+    /// Creates a new [PartialMmr] with default values.
+    fn default() -> Self {
+        let forest = 0;
+        let peaks = Vec::new();
+        let nodes = BTreeMap::new();
+        let track_latest = false;
+
+        Self { forest, peaks, nodes, track_latest }
+    }
+}
+
 impl PartialMmr {
     // CONSTRUCTORS
     // --------------------------------------------------------------------------------------------

miden-crypto/src/merkle/mmr/peaks.rs

@@ -34,6 +34,13 @@ pub struct MmrPeaks {
     peaks: Vec<RpoDigest>,
 }
 
+impl Default for MmrPeaks {
+    /// Returns new [`MmrPeaks`] instantiated from an empty vector of peaks and 0 leaves.
+    fn default() -> Self {
+        Self { num_leaves: 0, peaks: Vec::new() }
+    }
+}
+
 impl MmrPeaks {
     // CONSTRUCTOR
     // --------------------------------------------------------------------------------------------

miden-crypto/src/merkle/mmr/tests.rs

@@ -12,6 +12,23 @@ use crate::{
     merkle::{InOrderIndex, MerklePath, MerkleTree, MmrProof, NodeIndex, int_to_node},
 };
 
+#[test]
+fn tests_empty_mmr_peaks() {
+    let peaks = MmrPeaks::default();
+    assert_eq!(peaks.num_peaks(), 0);
+    assert_eq!(peaks.num_leaves(), 0);
+}
+
+#[test]
+fn test_empty_partial_mmr() {
+    let mmr = PartialMmr::default();
+    assert_eq!(mmr.num_leaves(), 0);
+    assert_eq!(mmr.forest(), 0);
+    assert_eq!(mmr.peaks(), MmrPeaks::default());
+    assert!(mmr.nodes.is_empty());
+    assert!(!mmr.track_latest);
+}
+
 #[test]
 fn test_position_equal_or_higher_than_leafs_is_never_contained() {
     let empty_forest = 0;