Add num.parse.

sdk/lib/core/num.dart

Index: sdk/lib/core/num.dart
diff --git a/sdk/lib/core/num.dart b/sdk/lib/core/num.dart
index 674ab2a469f22d96f265a20fdece0016e3bc52a7..d4eaf6116fa2a4bf68438c628061b95422a0582e 100644
--- a/sdk/lib/core/num.dart
+++ b/sdk/lib/core/num.dart
@@ -359,4 +359,33 @@ abstract class num implements Comparable<num> {
    *
    */
   String toString();
+
+  /**
+   * Parses a string containing a number literal into a number.
+   *
+   * The input string should be either one accepted by [int.parse] (with no

[floitsch, 2013/11/25 12:50:53]

won't work in dartdoc: []()

Not sure if much better, but here is my attempt.

The method first tries to read the [input] as integer (similar to [int.parse]
without radix). If that fails, it tries to parse the [input] as double (as in
[double.parse]). If that fails, too, it invokes [onError] with [input].

If no [onError] is supplied, it defaults to a function that throws a
[FormatException].

[Lasse Reichstein Nielsen, 2013/11/25 13:05:16]

That is better. Done.

+   * radix) or by [double.parse].
+   * If it would be accepted by [int.parse],
+   * the result is the integer that `int.parse` would return.
+   * Otherwise the result is the same result that `double.parse` would return.
+   *
+   * If the input is acceptable by neither `int.parse` nor `double.parse`,
+   * the result is found by calling [onError] with the input.
+   * If no [onError] is suppled, a [FormatException] is thrown.

[floitsch, 2013/11/25 12:50:53]

supplied

[Lasse Reichstein Nielsen, 2013/11/25 13:05:16]

Replaced by your wording above.

+   *
+   * For any number `n`, this function satisfies `n == num.parse(n.toString())`.

[floitsch, 2013/11/25 12:50:53]

any number `n`, not NaN, ...

or use identical(n, num.parse(n.toString()))

[Lasse Reichstein Nielsen, 2013/11/25 13:05:16]

Used identical. That's what the test tests too.

+   */
+  static num parse(String input, [num onError(String input)]) {
+    String source = input.trim();
+    // TODO(lrn): Optimize to detect format and result type in one check.
+    num result = int.parse(source, onError: _returnNull);
+    if (result != null) return result;
+    result = double.parse(source, _returnNull);
+    if (result != null) return result;
+    if (onError == null) throw new FormatException(input);
+    return onError(input);
+  }
+
+  /** Helper function for [parse]. */
+  static _returnNull(_) => null;
 }