Make String.fromCharCodes take start/end.

sdk/lib/core/string.dart

Index: sdk/lib/core/string.dart
diff --git a/sdk/lib/core/string.dart b/sdk/lib/core/string.dart
index 384b183c0b50af170b709dedb18605cc4e5eede3..9813ad0569c4f41ae957ac23930a9f1370fd5eb5 100644
--- a/sdk/lib/core/string.dart
+++ b/sdk/lib/core/string.dart
@@ -105,8 +105,17 @@ abstract class String implements Comparable<String>, Pattern {
    *     var clef = new String.fromCharCodes([0x1D11E]);
    *     clef.codeUnitAt(0); // 0xD834
    *     clef.codeUnitAt(1); // 0xDD1E
+   *
+   * If [start] is provided, the first `start` elements of `charCodes` are
+   * skipped. If `charCodes` has fewer than `start` elements in all, the
+   * result is an empty string. The `start` value must be non-negative.
+   *
+   * If [end] is provided, any elements of `charCodes` after the `end`'th are
+   * ignored. If `charCodes` has fewer than `end` elements, the `end` parameter
+   * has no effect.

[sra1, 2014/09/25 19:58:24]

Most APIs with a start and end are strict, requiring 

0 <= start <= end <= length.

This API is less strict.

Is this a deliberate choice to make this API inconsistent with sublist,
substring etc?
If there is not a strong reason, I'd prefer the libraries to be consistent.

[Lasse Reichstein Nielsen, 2014/09/25 20:01:08]

It is deliberate because the input is an iterable, not a list.
You are not expected to know the length of an iterable, so this works as if by
charcodes.take(end).skip(start).

We should probably not have allowed an iterable to being with, only lists.

[floitsch, 2014/09/25 20:08:46]

I agree with Stephen: start, end should have the same meaning everywhere.

    */
-  external factory String.fromCharCodes(Iterable<int> charCodes);
+  external factory String.fromCharCodes(Iterable<int> charCodes,
+                                        [int start = 0, int end]);
 
   /**
    * Allocates a new String for the specified [charCode].