Add String.replaceRange and use it in replaceFirst{,Mapped}.

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 625446fb8df99ec859c2052dbd6f32b0138ebb1b..1930e4f3ce91e9657d283cdfedbe649b70506f52 100644
--- a/sdk/lib/core/string.dart
+++ b/sdk/lib/core/string.dart
@@ -477,6 +477,19 @@ abstract class String implements Comparable<String>, Pattern {
   String replaceAllMapped(Pattern from, String replace(Match match));
 
   /**
+   * Replaces the substring from [start] to [end] with [replacement].
+   *
+   * Returns a new string equivalent to:
+   *
+   *     this.substring(0, start) + replacement + this.substring(end)
+   *
+   * The [start] and [end] indices must specify a valid range of this string.
+   * That is `0 <= start <= end <= this.length`.
+   * If [end] is omitted, it defaults to [length].
+   */
+  String replaceRange(String replacement, int start, [int end]);

[floitsch, 2015/02/23 14:36:35]

replaceRange in List takes the start-end first and the replacement as last
argument.
For consistency we should do the same here (even if that means that you cannot
omit 'end'.

[kevmoo, 2015/02/23 19:14:23]

Could we look into named arguments?

Then someone could do just from a start
Or just to and end
Or omit the 'replacement' and delete the section in the range.

Optional positional paint us in a corner in future API changes

[Lasse Reichstein Nielsen, 2015/02/25 12:09:09]

I agree that consistency wants to put the start/end arguments first (since it's
too late to fix the range functions, and we still don't have a slice operator).
Too late for named arguments (and they are annoying to use too).

As for painting us into a corner, please just fix the language, so it doesn't
have the annoying and arbitrary restriction against having both types of
optional parameters.

+
+  /**
    * Splits the string at matches of [pattern] and returns a list of substrings.
    *
    * Finds all the matches of `pattern` in this string,