private VectorExpressionWriter getWriter(TypeInfo colTypeInfo) throws HiveException {
    ExprNodeDesc columnDesc = new ExprNodeColumnDesc();
    columnDesc.setTypeInfo(colTypeInfo);
    VectorExpressionWriter vew = VectorExpressionWriterFactory
        .genVectorExpressionWritable(columnDesc);
    return vew;
  }
Unit tests for vector expression writers.
ql/src/test/org/apache/hadoop/hive/ql/exec/vector/expressions/TestVectorExpressionWriters.java