diff --git a/taichi/ir/type_factory.h b/taichi/ir/type_factory.h
index a273091579ea9..da4b772c8eb7f 100644
--- a/taichi/ir/type_factory.h
+++ b/taichi/ir/type_factory.h
@@ -13,38 +13,38 @@ class TypeFactory {
   // TODO(type): maybe it makes sense to let each get_X function return X*
   // instead of generic Type*
 
-  Type *get_primitive_type(PrimitiveTypeID id);
+  const Type *get_primitive_type(PrimitiveTypeID id);
 
-  PrimitiveType *get_primitive_int_type(int bits, bool is_signed = true);
+  const PrimitiveType *get_primitive_int_type(int bits, bool is_signed = true);
 
-  PrimitiveType *get_primitive_real_type(int bits);
+  const PrimitiveType *get_primitive_real_type(int bits);
 
-  Type *get_tensor_type(std::vector<int> shape, Type *element);
+  const Type *get_tensor_type(std::vector<int> shape, Type *element);
 
-  Type *get_pointer_type(Type *element, bool is_bit_pointer = false);
+  const Type *get_pointer_type(Type *element, bool is_bit_pointer = false);
 
-  Type *get_quant_int_type(int num_bits, bool is_signed, Type *compute_type);
+  const Type *get_quant_int_type(int num_bits, bool is_signed, Type *compute_type);
 
-  Type *get_quant_fixed_type(Type *digits_type,
+  const Type *get_quant_fixed_type(Type *digits_type,
                              Type *compute_type,
                              float64 scale);
 
-  Type *get_quant_float_type(Type *digits_type,
+  const Type *get_quant_float_type(Type *digits_type,
                              Type *exponent_type,
                              Type *compute_type);
 
-  BitStructType *get_bit_struct_type(
+  const BitStructType *get_bit_struct_type(
       PrimitiveType *physical_type,
       const std::vector<Type *> &member_types,
       const std::vector<int> &member_bit_offsets,
       const std::vector<int> &member_exponents,
       const std::vector<std::vector<int>> &member_exponent_users);
 
-  Type *get_quant_array_type(PrimitiveType *physical_type,
+  const Type *get_quant_array_type(PrimitiveType *physical_type,
                              Type *element_type,
                              int num_elements);
 
-  static DataType create_tensor_type(std::vector<int> shape, DataType element);
+  static const DataType create_tensor_type(std::vector<int> shape, DataType element);
 
  private:
   TypeFactory();