diff --git a/src/__stl__.h b/src/__stl__.h
index 7bbec654..f0185d23 100644
--- a/src/__stl__.h
+++ b/src/__stl__.h
@@ -16,6 +16,7 @@
 #include <string_view>
 #include <queue>
 #include <iomanip>
+#include <map>
 
 #include <thread>
 #include <atomic>
diff --git a/src/codeobject.h b/src/codeobject.h
index d285a53c..a4561ed0 100644
--- a/src/codeobject.h
+++ b/src/codeobject.h
@@ -23,7 +23,7 @@ struct ByteCode{
 };
 
 _Str pad(const _Str& s, const int n){
-    return s + _Str(n - s.size(), ' ');
+    return s + std::string(n - s.size(), ' ');
 }
 
 struct CodeObject {
diff --git a/src/compiler.h b/src/compiler.h
index 03b6665f..11f3abf7 100644
--- a/src/compiler.h
+++ b/src/compiler.h
@@ -260,7 +260,7 @@ public:
                         int ret = parser->eatName();
                         if(ret!=0) syntaxError("identifier is illegal, err " + std::to_string(ret));
                     } else {
-                        syntaxError("unknown character: " + _Str(1, c));
+                        syntaxError("unknown character: " + std::string(1, c));
                     }
                     return;
                 }
diff --git a/src/pocketpy.h b/src/pocketpy.h
index 193773d0..0e1a4483 100644
--- a/src/pocketpy.h
+++ b/src/pocketpy.h
@@ -83,7 +83,7 @@ void __initializeBuiltinFunctions(VM* _vm) {
         vm->__checkArgSize(args, 1);
         _Int i = vm->PyInt_AS_C(args[0]);
         if (i < 0 || i > 128) vm->valueError("chr() arg not in range(128)");
-        return vm->PyStr(_Str(1, (char)i));
+        return vm->PyStr(std::string(1, (char)i));
     });
 
     _vm->bindBuiltinFunc("ord", [](VM* vm, const pkpy::ArgList& args) {
diff --git a/src/str.h b/src/str.h
index 9c88b8c0..508ff45a 100644
--- a/src/str.h
+++ b/src/str.h
@@ -55,13 +55,12 @@ public:
 };
 
 
-std::unordered_map<std::string, std::shared_ptr<_StrMemory>> _strIntern;
+std::map<std::string, std::shared_ptr<_StrMemory>, std::less<>> _strIntern;
 
 
-struct _StrLiteral {
-    const char* _str;
-    size_t _len;
-    constexpr _StrLiteral(const char* str, size_t len) : _str(str), _len(len) {}
+class _StrLiteral : public std::string_view {
+public:
+    constexpr _StrLiteral(const char* str, size_t len) : std::string_view(str, len) {}
 };
 
 inline constexpr _StrLiteral operator "" _c(const char* str, size_t len){
@@ -74,36 +73,35 @@ private:
     bool interned = false;
 public:
     _Str(const _StrLiteral& s){
-        construct(std::string(s._str, s._len));
+        construct(s);
         intern();
     }
     _Str(const char* s){
-        construct(std::string(s));
+        construct(s);
     }
     _Str(const char* s, size_t len){
-        construct(std::string(s, len));
+        construct(std::string_view(s, len));
     }
-    _Str(int n, char fill){
-        construct(std::string(n, fill));
+    _Str(){
+        construct("");
     }
     _Str(const std::string& s){
         construct(s);
     }
-    _Str(std::string&& s){
-        construct(std::move(s));
-    }
-    _Str(){
-        construct(std::string());
-    }
     _Str(const _Str& s) : _s(s._s), interned(s.interned) {}
 
-    void construct(std::string s){
-        auto it = _strIntern.find(s);
+    // for move constructor, we do not check if the string is interned!!
+    _Str(std::string&& s){
+        this->_s = std::make_shared<_StrMemory>(std::move(s));
+    }
+
+    void construct(const std::string_view& sv){
+        auto it = _strIntern.find(sv);
         if(it != _strIntern.end()){
             this->_s = it->second;
             interned = true;
         }else{
-            this->_s = std::make_shared<_StrMemory>(std::move(s));
+            this->_s = std::make_shared<_StrMemory>(std::string(sv));
         }
     }