@Override
    public final double getDouble(int index) {
        double value = doubleValues()[index];
        if (Double.isNaN(value) && ! isMissing(index))  // NaN is valid as a missing value
            throw new UnsupportedOperationException("Value at " + index + " has no double representation");
        return value;
    }
Perform a fast lookup directly of the value as a double. This is faster than get(index).asDouble()
searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/evaluation/ArrayContext.java