presto-main/src/main/java/io/prestosql/sql/planner/TranslationMap.java/TranslationMap/copyMappingsFrom
class TranslationMap:    public void copyMappingsFrom(TranslationMap other)
    {
        checkArgument(other.fieldSymbols.length == fieldSymbols.length,
                "number of fields in other (%s) doesn't match number of expected fields (%s)",
                other.fieldSymbols.length,
                fieldSymbols.length);

        expressionToSymbols.putAll(other.expressionToSymbols);
        expressionToExpressions.putAll(other.expressionToExpressions);
        System.arraycopy(other.fieldSymbols, 0, fieldSymbols, 0, other.fieldSymbols.length);
    }