Adding AbstractNode class.

AbstractNode will provide interface for Operator and eventually
AbstractExpressions as well.

Note there are a few road blocks before the rest of the rewriter can be
changed to cleanly use abstract classes:
(1) Similarly abstract OperatorExpressions.
(2) We will have to find a good place to hide OpType, which is currently
an enum type (cannot be abstracted) and pervades the code base. This may
be solved by abstracting at the group level, but will have to look into
it.
(3) Need to clean up and separate interfaces between AbstractNode,
OperatorNode, and Operator classes.

src/include/optimizer/abstract_node.h

@@ -0,0 +1,117 @@
+//===----------------------------------------------------------------------===//
+//
+//                         Peloton
+//
+// abstract_node.h
+//
+// Identification: src/include/optimizer/abstract_node.h
+//
+// Copyright (c) 2015-16, Carnegie Mellon University Database Group
+//
+//===----------------------------------------------------------------------===//
+
+#pragma once
+
+#include "optimizer/property_set.h"
+#include "util/hash_util.h"
+
+#include <memory>
+#include <string>
+
+namespace peloton {
+namespace optimizer {
+
+enum class OpType {
+  Undefined = 0,
+  // Special match operators
+  Leaf,
+  // Logical ops
+  Get,
+  LogicalExternalFileGet,
+  LogicalQueryDerivedGet,
+  LogicalProjection,
+  LogicalFilter,
+  LogicalMarkJoin,
+  LogicalDependentJoin,
+  LogicalSingleJoin,
+  InnerJoin,
+  LeftJoin,
+  RightJoin,
+  OuterJoin,
+  SemiJoin,
+  LogicalAggregateAndGroupBy,
+  LogicalInsert,
+  LogicalInsertSelect,
+  LogicalDelete,
+  LogicalUpdate,
+  LogicalLimit,
+  LogicalDistinct,
+  LogicalExportExternalFile,
+  // Separate between logical and physical ops
+  LogicalPhysicalDelimiter,
+  // Physical ops
+  DummyScan, /* Dummy Physical Op for SELECT without FROM*/
+  SeqScan,
+  IndexScan,
+  ExternalFileScan,
+  QueryDerivedScan,
+  OrderBy,
+  PhysicalLimit,
+  Distinct,
+  InnerNLJoin,
+  LeftNLJoin,
+  RightNLJoin,
+  OuterNLJoin,
+  InnerHashJoin,
+  LeftHashJoin,
+  RightHashJoin,
+  OuterHashJoin,
+  Insert,
+  InsertSelect,
+  Delete,
+  Update,
+  Aggregate,
+  HashGroupBy,
+  SortGroupBy,
+  ExportExternalFile,
+};
+
+//===--------------------------------------------------------------------===//
+// Abstract Node
+//===--------------------------------------------------------------------===//
+//TODO(ncx): dependence on OperatorVisitor
+class OperatorVisitor;
+
+struct AbstractNode {
+  AbstractNode() {}
+
+  ~AbstractNode() {}
+
+  virtual void Accept(OperatorVisitor *v) const = 0;
+
+  virtual std::string GetName() const = 0;
+
+  // TODO(ncx): problematic dependence on OpType
+  virtual OpType GetType() const = 0;
+
+  virtual bool IsLogical() const = 0;
+
+  virtual bool IsPhysical() const = 0;
+
+  virtual hash_t Hash() const {
+    OpType t = GetType();
+    return HashUtil::Hash(&t);
+  }
+
+  virtual bool operator==(const AbstractNode &r) {
+    return GetType() == r.GetType();
+  }
+
+  virtual bool IsDefined() const { return node != nullptr; }
+
+ private:
+  std::shared_ptr<AbstractNode> node; 
+};
+
+}  // namespace optimizer
+}  // namespace peloton

src/include/optimizer/input_column_deriver.h

@@ -100,8 +100,8 @@ class InputColumnDeriver : public OperatorVisitor {
    * @brief Provide all tuple value expressions needed in the expression
    */
   void ScanHelper();
-  void AggregateHelper(const BaseOperatorNode *);
-  void JoinHelper(const BaseOperatorNode *op);
+  void AggregateHelper(const AbstractNode *);
+  void JoinHelper(const AbstractNode *op);
 
   /**
    * @brief Some operators, for example limit, directly pass down column

src/include/optimizer/operator_node.h

@@ -12,6 +12,7 @@
 
 #pragma once
 
+#include "optimizer/abstract_node.h"
 #include "optimizer/property_set.h"
 #include "util/hash_util.h"
 
@@ -21,103 +22,24 @@
 namespace peloton {
 namespace optimizer {
 
-enum class OpType {
-  Undefined = 0,
-  // Special match operators
-  Leaf,
-  // Logical ops
-  Get,
-  LogicalExternalFileGet,
-  LogicalQueryDerivedGet,
-  LogicalProjection,
-  LogicalFilter,
-  LogicalMarkJoin,
-  LogicalDependentJoin,
-  LogicalSingleJoin,
-  InnerJoin,
-  LeftJoin,
-  RightJoin,
-  OuterJoin,
-  SemiJoin,
-  LogicalAggregateAndGroupBy,
-  LogicalInsert,
-  LogicalInsertSelect,
-  LogicalDelete,
-  LogicalUpdate,
-  LogicalLimit,
-  LogicalDistinct,
-  LogicalExportExternalFile,
-  // Separate between logical and physical ops
-  LogicalPhysicalDelimiter,
-  // Physical ops
-  DummyScan, /* Dummy Physical Op for SELECT without FROM*/
-  SeqScan,
-  IndexScan,
-  ExternalFileScan,
-  QueryDerivedScan,
-  OrderBy,
-  PhysicalLimit,
-  Distinct,
-  InnerNLJoin,
-  LeftNLJoin,
-  RightNLJoin,
-  OuterNLJoin,
-  InnerHashJoin,
-  LeftHashJoin,
-  RightHashJoin,
-  OuterHashJoin,
-  Insert,
-  InsertSelect,
-  Delete,
-  Update,
-  Aggregate,
-  HashGroupBy,
-  SortGroupBy,
-  ExportExternalFile,
-};
-
 //===--------------------------------------------------------------------===//
 // Operator Node
 //===--------------------------------------------------------------------===//
 class OperatorVisitor;
 
-struct BaseOperatorNode {
-  BaseOperatorNode() {}
-
-  virtual ~BaseOperatorNode() {}
-
-  virtual void Accept(OperatorVisitor *v) const = 0;
-
-  virtual std::string GetName() const = 0;
-
-  virtual OpType GetType() const = 0;
-
-  virtual bool IsLogical() const = 0;
-
-  virtual bool IsPhysical() const = 0;
-
-  virtual std::vector<PropertySet> RequiredInputProperties() const {
-    return {};
-  }
-
-  virtual hash_t Hash() const {
-    OpType t = GetType();
-    return HashUtil::Hash(&t);
-  }
-
-  virtual bool operator==(const BaseOperatorNode &r) {
-    return GetType() == r.GetType();
-  }
-};
-
 // Curiously recurring template pattern
+// TODO(ncx): this templating would be nice to clean up
 template <typename T>
-struct OperatorNode : public BaseOperatorNode {
+struct OperatorNode : public AbstractNode {
+  OperatorNode() {}
+
+  virtual ~OperatorNode() {}
+
   void Accept(OperatorVisitor *v) const;
 
-  std::string GetName() const { return name_; }
+  virtual std::string GetName() const { return name_; }
 
-  OpType GetType() const { return type_; }
+  virtual OpType GetType() const { return type_; }
 
   bool IsLogical() const;
 
@@ -128,32 +50,26 @@ struct OperatorNode : public BaseOperatorNode {
   static OpType type_;
 };
 
-class Operator {
+class Operator : public AbstractNode {
  public:
   Operator();
 
-  Operator(BaseOperatorNode *node);
+  Operator(AbstractNode *node);
 
-  // Calls corresponding visitor to node
   void Accept(OperatorVisitor *v) const;
 
-  // Return name of operator
   std::string GetName() const;
 
-  // Return operator type
   OpType GetType() const;
 
-  // Operator contains Logical node
   bool IsLogical() const;
 
-  // Operator contains Physical node
   bool IsPhysical() const;
 
   hash_t Hash() const;
 
   bool operator==(const Operator &r);
 
-  // Operator contains physical or logical operator node
   bool IsDefined() const;
 
   template <typename T>
@@ -164,8 +80,12 @@ class Operator {
     return nullptr;
   }
 
+  static std::string name_;
+
+  static OpType type_;
+
  private:
-  std::shared_ptr<BaseOperatorNode> node;
+  std::shared_ptr<AbstractNode> node;
 };
 
 }  // namespace optimizer
@@ -174,8 +94,8 @@ class Operator {
 namespace std {
 
 template <>
-struct hash<peloton::optimizer::BaseOperatorNode> {
-  typedef peloton::optimizer::BaseOperatorNode argument_type;
+struct hash<peloton::optimizer::AbstractNode> {
+  typedef peloton::optimizer::AbstractNode argument_type;
   typedef std::size_t result_type;
   result_type operator()(argument_type const &s) const { return s.Hash(); }
 };