Optimize _GrowableArray._join and _StringBase._interpolate.

runtime/lib/string_patch.dart

Index: runtime/lib/string_patch.dart
diff --git a/runtime/lib/string_patch.dart b/runtime/lib/string_patch.dart
index 9a454b114da22988e9e3ccbb692b605011f8ea72..319be30bf3b8f86a90f717224ccd62c836b5eb94 100644
--- a/runtime/lib/string_patch.dart
+++ b/runtime/lib/string_patch.dart
@@ -530,28 +530,35 @@ class _StringBase {
   /**
    * Convert all objects in [values] to strings and concat them
    * into a result string.
+   * Modifies the input list if it contains non-`String` values.
    */
-  static String _interpolate(List<String> values) {
+  static String _interpolate(final List values) {
     final numValues = values.length;
-    _List stringList = new List<String>(numValues);
-    bool isOneByteString = true;
     int totalLength = 0;
     for (int i = 0; i < numValues; i++) {
-      var s = values[i].toString();
-      if (isOneByteString && (ClassID.getID(s) == ClassID.cidOneByteString)) {
+      final e = values[i];
+      final s = e.toString();
+      values[i] = s;

[Ivan Posva, 2014/09/16 14:57:32]

Again, non-properly looping loop. Please add comments as to what is going on and
ideally switch to a while statement.

[Lasse Reichstein Nielsen, 2014/09/18 09:30:37]

Comments added.
I've tried rewriting as while statement.
I', not sure it's more readable, but that might be author blindness.

The alternative I would normally use is:
  oneByteLoop: {
    for (...) {
       if (is not onebyteString) break oneByteLoop;
    }
    return _OneByteString._concatAll(...)
  }
  // handle non-onebyte case.

I am usually requested to rewrite that to something without labels, hence this
nested loop structure.

(Language feature request: for (...) {...} else { return ... } !)

+      if (ClassID.getID(s) == ClassID.cidOneByteString) {
         totalLength += s.length;
-      } else {
-        isOneByteString = false;
+        continue;
+      }
+      // Loops while the values convert to one-byte strings.
+      if (s is! String) {
+        throw new ArgumentError(s);
+      }
+      i++;
+      for (;i < numValues; i++) {
+        final e = values[i];
+        final s = e.toString();
+        values[i] = s;
         if (s is! String) {
           throw new ArgumentError(s);
         }
       }
-      stringList[i] = s;
-    }
-    if (isOneByteString) {
-      return _OneByteString._concatAll(stringList, totalLength);
+      return _concatRangeNative(values, 0, numValues);
     }
-    return _concatRangeNative(stringList, 0, stringList.length);
+    return _OneByteString._concatAll(values, totalLength);
   }
 
   Iterable<Match> allMatches(String string, [int start = 0]) {
@@ -669,6 +676,29 @@ class _OneByteString extends _StringBase implements String {
     return super == other;
   }
 
+  String operator +(String other) {
+    if (ClassID.getID(other) != ClassID.cidOneByteString) {
+      return super + other;
+    }
+    final thisLength = this.length;
+    final otherLength = other.length;
+    final length = thisLength + otherLength;
+    if (length > 128) {
+      final list = new _List(2);
+      list[0] = this;
+      list[1] = other;
+      return _concatAll(list, length);
+    }
+    final _OneByteString result = _allocate(length);
+    for (int i = 0; i < thisLength; i++) {
+      result._setAt(i, this.codeUnitAt(i));
+    }
+    for (int i = 0; i < otherLength; i++) {
+      result._setAt(thisLength + i, other.codeUnitAt(i));
+    }
+    return result;
+  }
+
   String _substringUncheckedNative(int startIndex, int endIndex)
       native "OneByteString_substringUnchecked";
 
@@ -690,11 +720,11 @@ class _OneByteString extends _StringBase implements String {
       // Native is quicker.
       return _StringBase._concatRangeNative(strings, 0, strings.length);
     }
-    var res = _OneByteString._allocate(totalLength);
+    final res = _OneByteString._allocate(totalLength);
     final stringsLength = strings.length;
     int rIx = 0;
     for (int i = 0; i < stringsLength; i++) {
-      _OneByteString e = strings[i];
+      final _OneByteString e = strings[i];
       final eLength = e.length;
       for (int s = 0; s < eLength; s++) {
         res._setAt(rIx++, e.codeUnitAt(s));