# convert method

List<int> convert (String string, [ int start = 0, int end ])
override

Converts `string` to its UTF-8 code units (a list of unsigned 8-bit integers).

If `start` and `end` are provided, only the substring `string.substring(start, end)` is converted.

## Implementation

    List<int> convert(String string, [int start = 0, int end]) {
      var stringLength = string.length;
      end = RangeError.checkValidRange(start, end, stringLength);
      var length = end - start;
      if (length == 0) return Uint8List(0);
      // Create a new encoder with a length that is guaranteed to be big enough.
      // A single code unit uses at most 3 bytes, a surrogate pair at most 4.
      var encoder = _Utf8Encoder.withBufferSize(length * 3);
      var endPosition = encoder._fillBuffer(string, start, end);
      assert(endPosition >= end - 1);
      if (endPosition != end) {
        // Encoding skipped the last code unit.
        // That can only happen if the last code unit is a leadsurrogate.
        // Force encoding of the lead surrogate by itself.
        var lastCodeUnit = string.codeUnitAt(end - 1);
        assert(_isLeadSurrogate(lastCodeUnit));
        // We use a non-surrogate as `nextUnit` so that _writeSurrogate just
        // writes the lead-surrogate.
        var wasCombined = encoder._writeSurrogate(lastCodeUnit, 0);
        assert(!wasCombined);
      }
      return encoder._buffer.sublist(0, encoder._bufferIndex);
    }