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operator [] method
Length operator [](Returns the object at the given index in the list or throws a RangeError if index is out of bounds.
Source
Length operator [](int index) {
  if (index < 0 || index >= length) throw new RangeError.index(index, this);
  return getItem(index);
}
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Licensed under the Creative Commons Attribution-ShareAlike License v4.0.
 https://api.dartlang.org/stable/1.24.3/dart-svg/LengthList/operator_get.html