# RuneIterator.at constructor

RuneIterator.at(String string, int index)

Create an iterator positioned before the `index`th code unit of the string.

When created, there is no current value. A moveNext will use the rune starting at `index` the current value, and a movePrevious will use the rune ending just before `index` as the the current value.

The `index` position must not be in the middle of a surrogate pair.

## Implementation

    RuneIterator.at(String string, int index)
        : string = string,
          _position = index,
          _nextPosition = index {
      RangeError.checkValueInInterval(index, 0, string.length);
      _checkSplitSurrogate(index);
    }