diff --git a/Package.resolved b/Package.resolved
index fde41db..975135d 100644
--- a/Package.resolved
+++ b/Package.resolved
@@ -1,21 +1,12 @@
 {
   "pins" : [
-    {
-      "identity" : "swiftui-gesture-velocity",
-      "kind" : "remoteSourceControl",
-      "location" : "https://github.com/FluidGroup/swiftui-gesture-velocity",
-      "state" : {
-        "revision" : "9c83f8995f9e5efc29db2fca4b9ff058283f1603",
-        "version" : "1.0.0"
-      }
-    },
     {
       "identity" : "swiftui-support",
       "kind" : "remoteSourceControl",
       "location" : "https://github.com/FluidGroup/swiftui-support",
       "state" : {
-        "revision" : "8ef53190c33bd345e7a95ef504dafe0f85ad9c4d",
-        "version" : "0.4.1"
+        "revision" : "c610c1e46c14c4660beb4ef7fe0241941dbecdc6",
+        "version" : "0.5.0"
       }
     }
   ],
diff --git a/Sources/DynamicList/DynamicListView.swift b/Sources/DynamicList/DynamicListView.swift
index 37406a5..12a3555 100644
--- a/Sources/DynamicList/DynamicListView.swift
+++ b/Sources/DynamicList/DynamicListView.swift
@@ -608,3 +608,4 @@ extension EnvironmentValues {
     set { self[CellContextKey.self] = newValue }
   }
 }
+
diff --git a/Sources/DynamicList/NSDiffableDataSourceSnapshot+Unique.swift b/Sources/DynamicList/NSDiffableDataSourceSnapshot+Unique.swift
new file mode 100644
index 0000000..3c2053c
--- /dev/null
+++ b/Sources/DynamicList/NSDiffableDataSourceSnapshot+Unique.swift
@@ -0,0 +1,61 @@
+
+import UIKit
+
+public enum DiffableDataSourceError: Error {
+  case duplicatedSectionIdentifiers(Set<AnyHashable>)
+  case duplicatedItemIdentifiers(Set<AnyHashable>)
+}
+
+extension NSDiffableDataSourceSnapshot {
+
+  public mutating func safeAppendSections(
+    _ sections: [SectionIdentifierType]
+  ) throws {
+
+    var sectionSet: Set<SectionIdentifierType> = []
+
+    for section in sections {
+      let (inserted, _) = sectionSet.insert(section)
+      guard inserted else {
+        throw DiffableDataSourceError.duplicatedSectionIdentifiers([section])
+      }
+    }
+
+
+    var set = Set(sectionIdentifiers)
+    set.formIntersection(sections)
+
+    if set.isEmpty {
+      appendSections(sections)
+    } else {
+      throw DiffableDataSourceError.duplicatedSectionIdentifiers(set)
+    }
+
+  }
+
+  public mutating func safeAppendItems(
+    _ items: [ItemIdentifierType],
+    intoSection sectionIdentifier: SectionIdentifierType? = nil
+  ) throws {
+
+    var itemSet: Set<ItemIdentifierType> = []
+
+    for item in items {
+      let (inserted, _) = itemSet.insert(item)
+      guard inserted else {
+        throw DiffableDataSourceError.duplicatedItemIdentifiers([item])
+      }
+    }
+
+    var set = Set(itemIdentifiers)
+    set.formIntersection(items)
+
+    if set.isEmpty {
+      appendItems(items, toSection: sectionIdentifier)
+    } else {
+      throw DiffableDataSourceError.duplicatedItemIdentifiers(set)
+    }
+
+  }
+
+}
diff --git a/Tests/DynamicListTests/swift_dynamic_listTests.swift b/Tests/DynamicListTests/swift_dynamic_listTests.swift
index 0187cc8..e4ffaef 100644
--- a/Tests/DynamicListTests/swift_dynamic_listTests.swift
+++ b/Tests/DynamicListTests/swift_dynamic_listTests.swift
@@ -1,12 +1,38 @@
 import XCTest
+
 @testable import DynamicList
 
 final class swift_dynamic_listTests: XCTestCase {
-    func testExample() throws {
-        // XCTest Documenation
-        // https://developer.apple.com/documentation/xctest
+  func testDiffable_append_duplicated() throws {
+
+    var snapshot = NSDiffableDataSourceSnapshot<String, Int>()
+    snapshot.appendSections(["A"])
+
+    do {
+      try snapshot.safeAppendItems([0, 0])
+      XCTFail()
+    } catch {
 
-        // Defining Test Cases and Test Methods
-        // https://developer.apple.com/documentation/xctest/defining_test_cases_and_test_methods
     }
+  }
+
+  func testDiffable_append_duplicated_2() throws {
+
+    var snapshot = NSDiffableDataSourceSnapshot<String, Int>()
+    snapshot.appendSections(["A"])
+    snapshot.appendItems([0])
+
+    do {
+      try snapshot.safeAppendItems([0])
+      XCTFail()
+    } catch {
+
+    }
+  }
+
+  func testIntersect() throws {
+
+    XCTAssertEqual(Set([1,2]).intersection([3,4]).isEmpty, true)
+
+  }
 }