optimize `str`'s iterator

include/pocketpy/iter.h

@@ -33,7 +33,7 @@ struct StringIter{
     PY_CLASS(StringIter, builtins, "_string_iterator")
     PyObject* ref;
     Str* str;
-    int index;
+    int index;      // byte index
 
     StringIter(PyObject* ref) : ref(ref), str(&PK_OBJ_GET(Str, ref)), index(0) {}
 
@@ -43,7 +43,7 @@ struct StringIter{
 };
 
 struct Generator{
-    PY_CLASS(Generator, builtins, "_generator")
+    PY_CLASS(Generator, builtins, "generator")
     Frame frame;
     int state;      // 0,1,2
     List s_backup;

src/iter.cpp

@@ -32,9 +32,11 @@ namespace pkpy{
         vm->bind__iter__(PK_OBJ_GET(Type, type), [](VM* vm, PyObject* obj){ return obj; });
         vm->bind__next__(PK_OBJ_GET(Type, type), [](VM* vm, PyObject* obj){
             StringIter& self = _CAST(StringIter&, obj);
-            // TODO: optimize this... operator[] is of O(n) complexity
-            if(self.index == self.str->u8_length()) return vm->StopIteration;
-            return VAR(self.str->u8_getitem(self.index++));
+            if(self.index == self.str->size) return vm->StopIteration;
+            int start = self.index;
+            int len = utf8len(self.str->data[self.index]);
+            self.index += len;
+            return VAR(self.str->substr(start, len));
         });
     }
 

tests/04_str.py

@@ -117,4 +117,21 @@ assert a.rjust(5, '0') == '00123'
 assert a.ljust(5) == '123  '
 assert a.ljust(5, '0') == '12300'
 
-assert '\x30\x31\x32' == '012'
+assert '\x30\x31\x32' == '012'
+
+a = 'abcd'
+assert list(a) == ['a', 'b', 'c', 'd']
+a = '测试'
+assert list(a) == ['测', '试']
+a = 'a测b试c'
+assert list(a) == ['a', '测', 'b', '试', 'c']
+a = 'a测b试'
+assert list(a) == ['a', '测', 'b', '试']
+a = '测b试c'
+assert list(a) == ['测', 'b', '试', 'c']
+a = '测b'
+assert list(a) == ['测', 'b']
+a = 'b'
+assert list(a) == ['b']
+a = '测'
+assert list(a) == ['测']