Add copy function in IShaderProperty, and implement this in all property classes

com.unity.shadergraph/Editor/Data/Graphs/AbstractShaderProperty.cs

 
         public abstract PreviewProperty GetPreviewMaterialProperty();
         public abstract INode ToConcreteNode();
+        public abstract IShaderProperty Copy();
     }
 }

com.unity.shadergraph/Editor/Data/Graphs/BooleanShaderProperty.cs

         {
             return new BooleanNode { value = new Toggle(value) };
         }
+
+        public override IShaderProperty Copy()
+        {
+            var copied = new BooleanShaderProperty();
+            copied.displayName = displayName;
+            copied.value = value;
+            return copied;
+        }
     }
 }

com.unity.shadergraph/Editor/Data/Graphs/ColorShaderProperty.cs

         {
             return new ColorNode { color = new ColorNode.Color(value, colorMode) };
         }
+
+        public override IShaderProperty Copy()
+        {
+            var copied = new ColorShaderProperty();
+            copied.displayName = displayName;
+            copied.value = value;
+            return copied;
+        }
     }
 }

com.unity.shadergraph/Editor/Data/Graphs/CubemapShaderProperty.cs

         {
             return new CubemapAssetNode { cubemap = value.cubemap };
         }
+
+        public override IShaderProperty Copy()
+        {
+            var copied = new CubemapShaderProperty();
+            copied.displayName = displayName;
+            copied.value = value;
+            return copied;
+        }
     }
 }

com.unity.shadergraph/Editor/Data/Graphs/IShaderProperty.cs

 
         PreviewProperty GetPreviewMaterialProperty();
         INode ToConcreteNode();
+        IShaderProperty Copy();
     }
 }

com.unity.shadergraph/Editor/Data/Graphs/Matrix2ShaderProperty.cs

                 row0 = new Vector2(value.m00, value.m01), 
                 row1 = new Vector2(value.m10, value.m11)
             };
-        } 
+        }
+
+        public override IShaderProperty Copy()
+        {
+            var copied = new Matrix2ShaderProperty();
+            copied.displayName = displayName;
+            copied.value = value;
+            return copied;
+        }
     }
 }

com.unity.shadergraph/Editor/Data/Graphs/Matrix3ShaderProperty.cs

                 row2 = new Vector3(value.m20, value.m21, value.m22)
             };
         }
+
+        public override IShaderProperty Copy()
+        {
+            var copied = new Matrix3ShaderProperty();
+            copied.displayName = displayName;
+            copied.value = value;
+            return copied;
+        }
     }
 }

com.unity.shadergraph/Editor/Data/Graphs/Matrix4ShaderProperty.cs

                 row3 = new Vector4(value.m30, value.m31, value.m32, value.m33)
             };
         }
+
+        public override IShaderProperty Copy()
+        {
+            var copied = new Matrix4ShaderProperty();
+            copied.displayName = displayName;
+            copied.value = value;
+            return copied;
+        }
     }
 }

com.unity.shadergraph/Editor/Data/Graphs/MatrixShaderProperty.cs

         public override PreviewProperty GetPreviewMaterialProperty()
         {
             return default(PreviewProperty);
-        }        
+        }
     }
 }

com.unity.shadergraph/Editor/Data/Graphs/SamplerStateShaderProperty.cs

-using System;
+using System;
 using UnityEditor.Graphing;
 using UnityEngine;
 
         public override INode ToConcreteNode()
         {
             return new SamplerStateNode();
+        }
+
+        public override IShaderProperty Copy()
+        {
+            var copied = new SamplerStateShaderProperty();
+            copied.displayName = displayName;
+            copied.value = value;
+            return copied;
         }
     }
 }

com.unity.shadergraph/Editor/Data/Graphs/TextureShaderProperty.cs

-using System;
+using System;
 using System.Text;
 using UnityEditor.Graphing;
 using UnityEngine;
         public override INode ToConcreteNode()
         {
             return new Texture2DAssetNode { texture = value.texture };
+        }
+
+        public override IShaderProperty Copy()
+        {
+            var copied = new TextureShaderProperty();
+            copied.displayName = displayName;
+            copied.value = value;
+            return copied;
         }
     }
 }

com.unity.shadergraph/Editor/Data/Graphs/Vector1ShaderProperty.cs

                     return node;
             }
         }
+
+        public override IShaderProperty Copy()
+        {
+            var copied = new Vector1ShaderProperty();
+            copied.displayName = displayName;
+            copied.value = value;
+            return copied;
+        }
     }
 }

com.unity.shadergraph/Editor/Data/Graphs/Vector2ShaderProperty.cs

             node.FindInputSlot<Vector1MaterialSlot>(Vector2Node.InputSlotYId).value = value.y;
             return node;
         }
+
+        public override IShaderProperty Copy()
+        {
+            var copied = new Vector2ShaderProperty();
+            copied.displayName = displayName;
+            copied.value = value;
+            return copied;
+        }
     }
 }

com.unity.shadergraph/Editor/Data/Graphs/Vector3ShaderProperty.cs

             node.FindInputSlot<Vector1MaterialSlot>(Vector3Node.InputSlotZId).value = value.z;
             return node;
         }
+
+        public override IShaderProperty Copy()
+        {
+            var copied = new Vector3ShaderProperty();
+            copied.displayName = displayName;
+            copied.value = value;
+            return copied;
+        }
     }
 }

com.unity.shadergraph/Editor/Data/Graphs/Vector4ShaderProperty.cs

             node.FindInputSlot<Vector1MaterialSlot>(Vector4Node.InputSlotWId).value = value.w;
             return node;
         }
+
+        public override IShaderProperty Copy()
+        {
+            var copied = new Vector4ShaderProperty();
+            copied.displayName = displayName;
+            copied.value = value;
+            return copied;
+        }
     }
 }

com.unity.shadergraph/Editor/Drawing/Views/MaterialGraphView.cs

             if (copyGraph == null)
                 return;
 
+            // Make new properties from the copied graph
-
-                IShaderProperty copiedProperty = null;
-
-                if (property is Vector1ShaderProperty)
-                {
-                    copiedProperty = new Vector1ShaderProperty();
-                    (copiedProperty as Vector1ShaderProperty).value = (property as Vector1ShaderProperty).value;
-                }
-                else if (property is Vector2ShaderProperty)
-                {
-                    copiedProperty = new Vector2ShaderProperty();
-                    (copiedProperty as Vector2ShaderProperty).value = (property as Vector2ShaderProperty).value;
-                }
-                else if (property is Vector3ShaderProperty)
-                {
-                    copiedProperty = new Vector3ShaderProperty();
-                    (copiedProperty as Vector3ShaderProperty).value = (property as Vector3ShaderProperty).value;
-                }
-                else if (property is Vector4ShaderProperty)
-                {
-                    copiedProperty = new Vector4ShaderProperty();
-                    (copiedProperty as Vector4ShaderProperty).value = (property as Vector4ShaderProperty).value;
-                }
-                else if (property is ColorShaderProperty)
-                {
-                    copiedProperty = new ColorShaderProperty();
-                    (copiedProperty as ColorShaderProperty).value = (property as ColorShaderProperty).value;
-                }
-                else if (property is TextureShaderProperty)
-                {
-                    copiedProperty = new TextureShaderProperty();
-                    (copiedProperty as TextureShaderProperty).value = (property as TextureShaderProperty).value;
-                }
-                else if (property is CubemapShaderProperty)
-                {
-                    copiedProperty = new CubemapShaderProperty();
-                    (copiedProperty as CubemapShaderProperty).value = (property as CubemapShaderProperty).value;
-                }
-                else if (property is BooleanShaderProperty)
-                {
-                    copiedProperty = new BooleanShaderProperty();
-                    (copiedProperty as BooleanShaderProperty).value = (property as BooleanShaderProperty).value;
-                }
-
+                IShaderProperty copiedProperty = property.Copy();
                 copiedProperty.displayName = propertyName;
                 graphView.graph.AddShaderProperty(copiedProperty);
             }