Use Pattern.matchAsPrefix to let String.indexOf/lastIndexOf/startsWith accept Pattern.

runtime/lib/string_patch.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 patch class String {
   /* patch */ factory String.fromCharCodes(Iterable<int> charCodes) {
     return _StringBase.createFromCharCodes(charCodes);
   }
 }
 
@@ skipping 95 matching lines @@
         return 1;
       }
     }
     if (thisLength < otherLength) return -1;
     if (thisLength > otherLength) return 1;
     return 0;
   }
 
   bool _substringMatches(int start, String other) {
     if (other.isEmpty) return true;
-    if ((start < 0) || (start >= this.length)) {
-      return false;
-    }
     final int len = other.length;
-    if ((start + len) > this.length) {
+    if ((start < 0) || (start + len > this.length)) {
       return false;
     }
     for (int i = 0; i < len; i++) {
       if (this.codeUnitAt(i + start) != other.codeUnitAt(i)) {
         return false;
       }
     }
     return true;
   }
 
   bool endsWith(String other) {
     return _substringMatches(this.length - other.length, other);
   }
 
-  bool startsWith(String other) {
-    return _substringMatches(0, other);
+  bool startsWith(Pattern pattern) {
+    if (pattern is String) {
+      return _substringMatches(0, pattern);
+    }
+    return pattern.matchAsPrefix(this, 0) != null;
   }
 
-  int indexOf(String other, [int start = 0]) {
-    if (other.isEmpty) {
-      return start < this.length ? start : this.length;
+  int indexOf(Pattern pattern, [int start = 0]) {
+    if (start < 0 || start > this.length) {
+      throw new RangeError.range(start, 0, this.length);
     }
-    if ((start < 0) || (start >= this.length)) {
+    if (pattern is String) {
+      String other = pattern;
+      int maxIndex = this.length - other.length;
+      // Consider using an efficient string search (e.g. BMH).

[floitsch, 2013/06/13 11:54:58]

Make this a TODO.

[Lasse Reichstein Nielsen, 2013/06/13 12:37:49]

Done.

+      for (int index = start; index <= maxIndex; index++) {
+        if (_substringMatches(index, other)) {
+          return index;
+        }
+      }
       return -1;
     }
-    int len = this.length - other.length + 1;
-    for (int index = start; index < len; index++) {
-      if (_substringMatches(index, other)) {
-        return index;
-      }
+    for (int i = start; i <= this.length; i++) {
+      if (pattern.matchAsPrefix(this, i) != null) return i;
     }
     return -1;
   }
 
-  int lastIndexOf(String other, [int start = null]) {
-    if (start == null) start = length - 1;
-    if (other.isEmpty) {
-      return min(this.length, start);
+  int lastIndexOf(Pattern pattern, [int start = null]) {
+    if (start == null) {
+      start = this.length;
+    } else if (start < 0 || start > this.length) {
+      throw new RangeError.range(start, 0, this.length);
     }
-    if (start >= this.length) {
-      start = this.length - 1;
+    if (pattern is String) {
+      String other = pattern;
+      int maxIndex = this.length - other.length;
+      if (maxIndex < start) start = maxIndex;
+      for (int index = start; index >= 0; index--) {
+        if (_substringMatches(index, other)) {
+          return index;
+        }
+      }
+      return -1;
     }
-    for (int index = start; index >= 0; index--) {
-      if (_substringMatches(index, other)) {
-        return index;
-      }
+    for (int i = start; i >= 0; i--) {
+      // This has quadratic behavior because matchAsPrefix tries to find a later

[floitsch, 2013/06/13 11:54:58]

TODO(..): currently this has quadratic behavior because matchAsPrefix tries to
find ...

[Lasse Reichstein Nielsen, 2013/06/13 12:37:49]

Done.

+      // match too. Optimize matchAsPrefix to avoid this.
+      if (pattern.matchAsPrefix(this, i) != null) return i;
     }
     return -1;
   }
 
   String substring(int startIndex, [int endIndex]) {
     if (endIndex == null) endIndex = this.length;
 
     if ((startIndex < 0) || (startIndex > this.length)) {
       throw new RangeError.value(startIndex);
     }
@@ skipping 437 matching lines @@
 class _CodeUnits extends Object with ListMixin<int>,
                                      UnmodifiableListMixin<int> {
   /** The string that this is the code units of. */
   String _string;
 
   _CodeUnits(this._string);
 
   int get length => _string.length;
   int operator[](int i) => _string.codeUnitAt(i);
 }