private void handleCouldNotInstantiateVectorExpression(Class<?> vectorClass, TypeInfo returnType,
      DataTypePhysicalVariation dataTypePhysicalVariation, Object[] arguments) throws HiveException {
    String displayString = "Could not instantiate vector expression class " + vectorClass.getName() +
        " for arguments " + Arrays.toString(arguments) + " return type " +
        VectorExpression.getTypeName(returnType, dataTypePhysicalVariation);
    throw new HiveException(displayString);
  }
Used as a fast path for operations that don't modify their input, like unary +
and casting boolean to long. IdentityExpression and its children are always
projections.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/VectorizationContext.java