add ssz clone

src/tests.zig

@@ -2574,6 +2574,57 @@ test "utils.List dynamic-item: offsets decrease" {
     try expectError(error.OffsetOrdering, L.sszDecode(&buf, &out, std.testing.allocator));
 }
 
+test "utils.List.clone copies backing storage independently" {
+    const L = utils.List([]const u8, 4);
+    var data = try L.init(std.testing.allocator);
+    defer data.deinit();
+    try data.append("aa");
+    try data.append("bb");
+
+    var cloned = try data.clone(std.testing.allocator);
+    defer cloned.deinit();
+
+    try expect(cloned.len() == data.len());
+    try expect(cloned.inner.items.ptr != data.inner.items.ptr);
+    try expect(std.mem.eql(u8, (try cloned.get(0)), "aa"));
+    try expect((try cloned.get(0)).ptr == (try data.get(0)).ptr);
+}
+
+test "utils.List.clone with variable-sized struct items" {
+    const L = utils.List(Pastry, 8);
+    var data = try L.init(std.testing.allocator);
+    defer data.deinit();
+    try data.append(pastries[0]);
+    try data.append(pastries[1]);
+
+    var cloned = try data.clone(std.testing.allocator);
+    defer cloned.deinit();
+
+    try expect(cloned.len() == 2);
+    try expect(cloned.inner.items.ptr != data.inner.items.ptr);
+    try expect((try cloned.get(0)).weight == pastries[0].weight);
+    try expect((try cloned.get(1)).weight == pastries[1].weight);
+    // Item-level []const u8 fields stay borrowed (shallow item copy).
+    try expect((try cloned.get(0)).name.ptr == pastries[0].name.ptr);
+    try expect((try cloned.get(1)).name.ptr == pastries[1].name.ptr);
+}
+
+test "utils.Bitlist.clone copies backing storage independently" {
+    const B = utils.Bitlist(32);
+    var data = try B.init(std.testing.allocator);
+    defer data.deinit();
+    try data.append(true);
+    try data.append(false);
+    try data.append(true);
+
+    var cloned = try data.clone(std.testing.allocator);
+    defer cloned.deinit();
+
+    try expect(cloned.eql(&data));
+    try cloned.set(0, false);
+    try expect((try data.get(0)) == true);
+}
+
 test {
     _ = @import("beacon_tests.zig");
 }

src/utils.zig

@@ -35,6 +35,14 @@ pub fn List(T: type, comptime N: usize) type {
             try serialize([]const Item, self.constSlice(), l, allocator);
         }
 
+        /// Clones this list's backing storage; item ownership matches normal List values.
+        pub fn clone(self: *const Self, allocator: Allocator) !Self {
+            var cloned = try Self.init(allocator);
+            errdefer cloned.deinit();
+            try cloned.inner.appendSlice(allocator, self.inner.items);
+            return cloned;
+        }
+
         pub fn isFixedSizeObject() bool {
             return false;
         }
@@ -254,6 +262,15 @@ pub fn Bitlist(comptime N: usize) type {
             }
         }
 
+        /// Clones this bitlist's backing storage.
+        pub fn clone(self: *const Self, allocator: Allocator) !Self {
+            var cloned = try Self.init(allocator);
+            errdefer cloned.deinit();
+            cloned.length = self.length;
+            try cloned.inner.appendSlice(allocator, self.inner.items);
+            return cloned;
+        }
+
         pub fn sszDecode(serialized: []const u8, out: *Self, allocator: ?std.mem.Allocator) !void {
             const alloc = allocator orelse return error.AllocatorRequired;
             out.* = try init(alloc);