diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4e9c2b91..d2cee2ab 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -18,9 +18,9 @@ if(NOT ${PREBUILD_RESULT} EQUAL 0)
 endif()
 
 if(MSVC)
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /GR- /EHsc /utf-8 /O2")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /EHsc /utf-8 /O2")
 else()
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fno-rtti -fexceptions -O2")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fexceptions -O2")
 endif()
 
 include_directories(${CMAKE_CURRENT_LIST_DIR}/include)
diff --git a/README.md b/README.md
index 818a48ed..6a4a5f61 100644
--- a/README.md
+++ b/README.md
@@ -40,7 +40,6 @@ To compile it with your project, these flags must be set:
 
 + `--std=c++17` flag must be set
 + Exception must be enabled
-+ RTTI is not required
 
 ### Example
 
diff --git a/build.sh b/build.sh
index 630e9e92..5c81603d 100644
--- a/build.sh
+++ b/build.sh
@@ -1,14 +1,16 @@
 python3 prebuild.py
 SRC=$(find src/ -name "*.cpp")
-FLAGS="-std=c++17 -fno-rtti -O2 -stdlib=libc++ -Wfatal-errors -Iinclude"
+FLAGS="-std=c++17 -O2 -stdlib=libc++ -Wfatal-errors -Iinclude"
 
 if [[ "$OSTYPE" == "darwin"* ]]; then
     LIB_EXTENSION=".dylib"
     FLAGS="$FLAGS -undefined dynamic_lookup"
+    LINK_FLAGS=""
 else
     LIB_EXTENSION=".so"
+    LINK_FLAGS="-Wl,-rpath=."
 fi
 clang++ $FLAGS -o libpocketpy$LIB_EXTENSION $SRC -fPIC -shared -ldl
 
 # compile main.cpp and link to libpocketpy.so
-clang++ $FLAGS -o main src2/main.cpp -L. -lpocketpy -Wl,-rpath=.
\ No newline at end of file
+clang++ $FLAGS -o main src2/main.cpp -L. -lpocketpy $LINK_FLAGS
\ No newline at end of file
diff --git a/build_web.sh b/build_web.sh
index bfc5738a..9ed30b58 100644
--- a/build_web.sh
+++ b/build_web.sh
@@ -4,4 +4,4 @@ rm -rf web/lib
 mkdir web/lib
 
 SRC=$(find src/ -name "*.cpp")
-em++ $SRC -Iinclude/ -fno-rtti -fexceptions -O3 -sEXPORTED_FUNCTIONS=_pkpy_new_repl,_pkpy_repl_input,_pkpy_new_vm -sEXPORTED_RUNTIME_METHODS=ccall -o web/lib/pocketpy.js
\ No newline at end of file
+em++ $SRC -Iinclude/ -fexceptions -O3 -sEXPORTED_FUNCTIONS=_pkpy_new_repl,_pkpy_repl_input,_pkpy_new_vm -sEXPORTED_RUNTIME_METHODS=ccall -o web/lib/pocketpy.js
\ No newline at end of file
diff --git a/c_bindings/test.c b/c_bindings/test.c
index c1c78905..7d65d147 100644
--- a/c_bindings/test.c
+++ b/c_bindings/test.c
@@ -413,11 +413,11 @@ int main(int argc, char** argv) {
 
     PRINT_TITLE("test py_repr");
     check(pkpy_eval(vm, "['1', 2, (3, '4')]"));
-    check(pkpy_py_repr(vm, -1));
+    check(pkpy_py_repr(vm));
     check(pkpy_to_string(vm, -1, &r_string));
     for(int i = 0; i < r_string.size; i++) putchar(r_string.data[i]);
     putchar('\n');
-    check(pkpy_pop(vm, 2));
+    check(pkpy_pop_top(vm));
     check(pkpy_stack_size(vm) == 0);
     return 0;
 }
diff --git a/docs/C-API/stack.md b/docs/C-API/stack.md
index e8d80a6d..88a426a1 100644
--- a/docs/C-API/stack.md
+++ b/docs/C-API/stack.md
@@ -6,6 +6,10 @@ order: 8
 
 ### Basic manipulation
 
++ `bool pkpy_dup(pkpy_vm*, int)`
+
+    Duplicate the value at the given index.
+
 + `bool pkpy_pop(pkpy_vm*, int)`
 
     Pop `n` values from the stack.
@@ -70,7 +74,7 @@ PK_EXPORT bool pkpy_is_none(pkpy_vm*, int i);
 
 + `pkpy_push_null(pkpy_vm*)`
 
-    Push a `PY_NULL` onto the stack.
+    Push a `PY_NULL` onto the stack. It is used for `pkpy_vectorcall`.
 
 + `pkpy_push_function(pkpy_vm*, const char* sig, pkpy_CFunction f)`
 
@@ -140,10 +144,10 @@ PK_EXPORT bool pkpy_is_none(pkpy_vm*, int i);
     ```
     [obj] -> [obj.<name> self]
     ```
-+ `bool pkpy_py_repr(pkpy_vm*, int i)`
++ `bool pkpy_py_repr(pkpy_vm*)`
 
-    Get the repr of the value at the given index and push it onto the stack.
+    Get the repr of the value at the top of the stack.
 
     ```
-    [..., value, ...] -> [..., value, ..., repr(value)]
+    [value] -> [repr(value)]
     ```
\ No newline at end of file
diff --git a/docs/quick-start/installation.md b/docs/quick-start/installation.md
index 3de66c02..28c4fa27 100644
--- a/docs/quick-start/installation.md
+++ b/docs/quick-start/installation.md
@@ -22,7 +22,6 @@ To compile it with your project, these flags must be set:
 
 + `--std=c++17` flag must be set
 + Exception must be enabled
-+ RTTI is not required
 
 ### Example
 
diff --git a/include/pocketpy/obj.h b/include/pocketpy/obj.h
index e4aa3e92..ac66d73b 100644
--- a/include/pocketpy/obj.h
+++ b/include/pocketpy/obj.h
@@ -61,11 +61,12 @@ struct Bytes{
         return _data != rhs._data;
     }
 
-    std::string str() const noexcept { return std::string(_data.begin(), _data.end()); }
+    Str str() const noexcept { return Str(_data.data(), _data.size()); }
 
     Bytes() : _data(), _ok(false) {}
     Bytes(std::vector<char>&& data) : _data(std::move(data)), _ok(true) {}
-    Bytes(const std::string& data) : _data(data.begin(), data.end()), _ok(true) {}
+    Bytes(const Str& data) : _data(data.begin(), data.end()), _ok(true) {}
+    Bytes(std::string_view sv): _data(sv.begin(), sv.end()), _ok(true) {}
     operator bool() const noexcept { return _ok; }
 };
 
diff --git a/include/pocketpy/pocketpy_c.h b/include/pocketpy/pocketpy_c.h
index 7e7a31ee..677aacc9 100644
--- a/include/pocketpy/pocketpy_c.h
+++ b/include/pocketpy/pocketpy_c.h
@@ -27,6 +27,7 @@ PK_EXPORT bool pkpy_exec(pkpy_vm*, const char* source);
 PK_EXPORT bool pkpy_exec_2(pkpy_vm*, const char* source, const char* filename, int mode, const char* module);
 
 /* Stack Manipulation */
+PK_EXPORT bool pkpy_dup(pkpy_vm*, int);
 PK_EXPORT bool pkpy_pop(pkpy_vm*, int);
 PK_EXPORT bool pkpy_pop_top(pkpy_vm*);
 PK_EXPORT bool pkpy_dup_top(pkpy_vm*);
@@ -75,7 +76,7 @@ PK_EXPORT bool pkpy_setglobal(pkpy_vm*, pkpy_CName);
 PK_EXPORT bool pkpy_eval(pkpy_vm*, const char* source);
 PK_EXPORT bool pkpy_unpack_sequence(pkpy_vm*, int size);
 PK_EXPORT bool pkpy_get_unbound_method(pkpy_vm*, pkpy_CName);
-PK_EXPORT bool pkpy_py_repr(pkpy_vm*, int i);
+PK_EXPORT bool pkpy_py_repr(pkpy_vm*);
 
 /* Error Handling */
 PK_EXPORT bool pkpy_error(pkpy_vm*, const char* name, pkpy_CString);
diff --git a/plugins/flutter/src/CMakeLists.txt b/plugins/flutter/src/CMakeLists.txt
index 3f2faf3d..0007b96f 100644
--- a/plugins/flutter/src/CMakeLists.txt
+++ b/plugins/flutter/src/CMakeLists.txt
@@ -13,12 +13,6 @@ add_library(pocketpy SHARED
   "pocketpy.cpp"
 )
 
-if (NOT MSVC)
-  target_compile_options(pocketpy PRIVATE -fno-rtti)
-else()
-  target_compile_options(pocketpy PRIVATE /GR- /EHsc)
-endif()
-
 set_target_properties(pocketpy PROPERTIES
   PUBLIC_HEADER pocketpy.h
   OUTPUT_NAME "pocketpy"
diff --git a/run_profile.sh b/run_profile.sh
index 18acc550..33b1cdcb 100644
--- a/run_profile.sh
+++ b/run_profile.sh
@@ -1,6 +1,6 @@
 python3 prebuild.py
 SRC=$(find src/ -name "*.cpp")
-clang++ -pg -O1 -std=c++17 -fno-rtti -stdlib=libc++ -Wfatal-errors -o main $SRC -Iinclude -ldl
+clang++ -pg -O1 -std=c++17 -stdlib=libc++ -Wfatal-errors -o main $SRC -Iinclude -ldl
 time ./main benchmarks/fib.py
 mv benchmarks/gmon.out .
 gprof pocketpy gmon.out > gprof.txt
diff --git a/run_tests.sh b/run_tests.sh
index 60dcb8ad..50b01a68 100644
--- a/run_tests.sh
+++ b/run_tests.sh
@@ -1,6 +1,6 @@
 python3 prebuild.py
 SRC=$(find src/ -name "*.cpp")
-clang++ -std=c++17 -fno-rtti --coverage -O1 -stdlib=libc++ -Wfatal-errors -o main src2/main.cpp $SRC -Iinclude -ldl
+clang++ -std=c++17 --coverage -O1 -stdlib=libc++ -Wfatal-errors -o main src2/main.cpp $SRC -Iinclude -ldl
 python3 scripts/run_tests.py
 rm -rf .coverage
 mkdir .coverage
diff --git a/src/pocketpy.cpp b/src/pocketpy.cpp
index 35d26daa..4a180cf3 100644
--- a/src/pocketpy.cpp
+++ b/src/pocketpy.cpp
@@ -916,7 +916,8 @@ void init_builtins(VM* _vm) {
 
     _vm->bind__hash__(_vm->tp_bytes, [](VM* vm, PyObject* obj) {
         const Bytes& self = _CAST(Bytes&, obj);
-        return (i64)std::hash<std::string>()(self.str());
+        std::string_view view(self.data(), self.size());
+        return (i64)std::hash<std::string_view>()(view);
     });
 
     _vm->bind__repr__(_vm->tp_bytes, [](VM* vm, PyObject* obj) {
diff --git a/src/pocketpy_c.cpp b/src/pocketpy_c.cpp
index ed4ed4c1..e3aba0fa 100644
--- a/src/pocketpy_c.cpp
+++ b/src/pocketpy_c.cpp
@@ -89,6 +89,16 @@ bool pkpy_exec_2(pkpy_vm* vm_handle, const char* source, const char* filename, i
     return res != nullptr;
 }
 
+bool pkpy_dup(pkpy_vm* vm_handle, int n){
+    VM* vm = (VM*) vm_handle;
+    PK_ASSERT_NO_ERROR()
+    PK_PROTECTED(
+        PyObject* item = stack_item(vm, n);
+        vm->s_data.push(item);
+    )
+    return true;
+}
+
 bool pkpy_pop(pkpy_vm* vm_handle, int n){
     VM* vm = (VM*) vm_handle;
     PK_ASSERT_NO_ERROR()
@@ -461,15 +471,15 @@ bool pkpy_get_unbound_method(pkpy_vm* vm_handle, pkpy_CName name){
     return true;
 }
 
-bool pkpy_py_repr(pkpy_vm* vm_handle, int i) {
+bool pkpy_py_repr(pkpy_vm* vm_handle) {
     VM* vm = (VM*) vm_handle;
     PK_ASSERT_NO_ERROR()
     PK_ASSERT_N_EXTRA_ELEMENTS(1)
+    PyObject* item = vm->s_data.top();
     PK_PROTECTED(
-        PyObject* item = stack_item(vm, i);
-        PyObject* repr = vm->py_repr(item);
-        vm->s_data.push(repr);
+        item = vm->py_repr(item);
     )
+    vm->s_data.top() = item;
     return true;
 }
 
diff --git a/tests/10_bytes.py b/tests/10_bytes.py
index f982fa1e..f1a0f0c9 100644
--- a/tests/10_bytes.py
+++ b/tests/10_bytes.py
@@ -3,3 +3,6 @@ assert a.encode() == b'12345'
 
 assert b'\xff\xee' != b'1234'
 assert b'\xff\xee' == b'\xff\xee'
+
+a = '测试123'
+assert a == a.encode().decode()
\ No newline at end of file