Add Model and Configurable interface. (#4945)

* Apply Configurable to objective functions.
* Apply Model to Learner and Regtree, gbm.
* Add Load/SaveConfig to objs.
* Refactor obj tests to use smart pointer.
* Dummy methods for Save/Load Model.

include/xgboost/generic_parameters.h

@@ -7,7 +7,7 @@
 
 #include <dmlc/parameter.h>
 #include <xgboost/logging.h>
-#include <xgboost/enum_class_param.h>
+#include <xgboost/parameter.h>
 
 #include <string>
 

include/xgboost/json.h

@@ -322,6 +322,9 @@ class Json {
   static void Dump(Json json, std::ostream* stream,
                    bool pretty = ConsoleLogger::ShouldLog(
                        ConsoleLogger::LogVerbosity::kDebug));
+  static void Dump(Json json, std::string* out,
+                   bool pretty = ConsoleLogger::ShouldLog(
+                       ConsoleLogger::LogVerbosity::kDebug));
 
   Json() : ptr_{new JsonNull} {}
 
@@ -400,6 +403,13 @@ class Json {
     return *ptr_ == *(rhs.ptr_);
   }
 
+  friend std::ostream& operator<<(std::ostream& os, Json const& j) {
+    std::string str;
+    Json::Dump(j, &str);
+    os << str;
+    return os;
+  }
+
  private:
   std::shared_ptr<Value> ptr_;
 };

include/xgboost/learner.h

@@ -16,6 +16,7 @@
 #include <xgboost/objective.h>
 #include <xgboost/feature_map.h>
 #include <xgboost/generic_parameters.h>
+#include <xgboost/model.h>
 
 #include <utility>
 #include <map>
@@ -41,7 +42,7 @@ namespace xgboost {
  *
  *  \endcode
  */
-class Learner : public rabit::Serializable {
+class Learner : public Model, public rabit::Serializable {
  public:
   /*! \brief virtual destructor */
   ~Learner() override = default;

include/xgboost/logging.h

@@ -1,9 +1,9 @@
 /*!
  * Copyright (c) 2015-2019 by Contributors
  * \file logging.h
- * \brief defines console logging options for xgboost.
- *  Use to enforce unified print behavior.
- *  For debug loggers, use LOG(INFO) and LOG(ERROR).
+ *
+ * \brief defines console logging options for xgboost.  Use to enforce unified print
+ *  behavior.
  */
 #ifndef XGBOOST_LOGGING_H_
 #define XGBOOST_LOGGING_H_

include/xgboost/model.h

@@ -0,0 +1,44 @@
+/*!
+ * Copyright (c) 2019 by Contributors
+ * \file model.h
+ * \brief Defines the abstract interface for different components in XGBoost.
+ */
+#ifndef XGBOOST_MODEL_H_
+#define XGBOOST_MODEL_H_
+
+namespace dmlc {
+class Stream;
+}  // namespace dmlc
+
+namespace xgboost {
+
+class Json;
+
+struct Model {
+  /*!
+   * \brief Save the model to stream.
+   * \param fo output write stream
+   */
+  virtual void SaveModel(dmlc::Stream* fo) const = 0;
+  /*!
+   * \brief Load the model from stream.
+   * \param fi input read stream
+   */
+  virtual void LoadModel(dmlc::Stream* fi) = 0;
+};
+
+struct Configurable {
+  /*!
+   * \brief Load configuration from JSON object
+   * \param in JSON object containing the configuration
+   */
+  virtual void LoadConfig(Json const& in) = 0;
+  /*!
+   * \brief Save configuration to JSON object
+   * \param out pointer to output JSON object
+   */
+  virtual void SaveConfig(Json* out) const = 0;
+};
+}  // namespace xgboost
+
+#endif  // XGBOOST_MODEL_H_

include/xgboost/objective.h

@@ -10,6 +10,7 @@
 #include <dmlc/registry.h>
 #include <xgboost/base.h>
 #include <xgboost/data.h>
+#include <xgboost/model.h>
 #include <xgboost/generic_parameters.h>
 #include <xgboost/host_device_vector.h>
 
@@ -21,7 +22,7 @@
 namespace xgboost {
 
 /*! \brief interface of objective function */
-class ObjFunction {
+class ObjFunction : public Configurable {
  protected:
   GenericParameter const* tparam_;
 

include/xgboost/parameter.h

@@ -5,10 +5,11 @@
  * \author Hyunsu Philip Cho
  */
 
-#ifndef XGBOOST_ENUM_CLASS_PARAM_H_
-#define XGBOOST_ENUM_CLASS_PARAM_H_
+#ifndef XGBOOST_PARAMETER_H_
+#define XGBOOST_PARAMETER_H_
 
 #include <dmlc/parameter.h>
+#include <xgboost/base.h>
 #include <string>
 #include <type_traits>
 
@@ -78,4 +79,27 @@ class FieldEntry<EnumClass> : public FieldEntry<int> {  \
 }  /* namespace parameter */  \
 }  /* namespace dmlc */
 
-#endif  // XGBOOST_ENUM_CLASS_PARAM_H_
+namespace xgboost {
+template <typename Type>
+struct XGBoostParameter : public dmlc::Parameter<Type> {
+ protected:
+  bool initialised_ {false};
+
+ public:
+  template <typename Container>
+  Args UpdateAllowUnknown(Container const& kwargs, bool* out_changed = nullptr) {
+    if (initialised_) {
+      return dmlc::Parameter<Type>::UpdateAllowUnknown(kwargs, out_changed);
+    } else {
+      auto unknown = dmlc::Parameter<Type>::InitAllowUnknown(kwargs);
+      if (out_changed) {
+        *out_changed = true;
+      }
+      initialised_ = true;
+      return unknown;
+    }
+  }
+};
+}  // namespace xgboost
+
+#endif  // XGBOOST_PARAMETER_H_

include/xgboost/tree_model.h

@@ -14,6 +14,7 @@
 #include <xgboost/data.h>
 #include <xgboost/logging.h>
 #include <xgboost/feature_map.h>
+#include <xgboost/model.h>
 
 #include <limits>
 #include <vector>
@@ -93,7 +94,7 @@ struct RTreeNodeStat {
  * \brief define regression tree to be the most common tree model.
  *  This is the data structure used in xgboost's major tree models.
  */
-class RegTree {
+class RegTree : public Model {
  public:
   /*! \brief auxiliary statistics of node to help tree building */
   using SplitCondT = bst_float;
@@ -289,38 +290,17 @@ class RegTree {
   const RTreeNodeStat& Stat(int nid) const {
     return stats_[nid];
   }
+
   /*!
    * \brief load model from stream
    * \param fi input stream
    */
-  void Load(dmlc::Stream* fi) {
-    CHECK_EQ(fi->Read(&param, sizeof(TreeParam)), sizeof(TreeParam));
-    nodes_.resize(param.num_nodes);
-    stats_.resize(param.num_nodes);
-    CHECK_NE(param.num_nodes, 0);
-    CHECK_EQ(fi->Read(dmlc::BeginPtr(nodes_), sizeof(Node) * nodes_.size()),
-             sizeof(Node) * nodes_.size());
-    CHECK_EQ(fi->Read(dmlc::BeginPtr(stats_), sizeof(RTreeNodeStat) * stats_.size()),
-             sizeof(RTreeNodeStat) * stats_.size());
-    // chg deleted nodes
-    deleted_nodes_.resize(0);
-    for (int i = param.num_roots; i < param.num_nodes; ++i) {
-      if (nodes_[i].IsDeleted()) deleted_nodes_.push_back(i);
-    }
-    CHECK_EQ(static_cast<int>(deleted_nodes_.size()), param.num_deleted);
-  }
+  void LoadModel(dmlc::Stream* fi) override;
   /*!
    * \brief save model to stream
    * \param fo output stream
    */
-  void Save(dmlc::Stream* fo) const {
-    CHECK_EQ(param.num_nodes, static_cast<int>(nodes_.size()));
-    CHECK_EQ(param.num_nodes, static_cast<int>(stats_.size()));
-    fo->Write(&param, sizeof(TreeParam));
-    CHECK_NE(param.num_nodes, 0);
-    fo->Write(dmlc::BeginPtr(nodes_), sizeof(Node) * nodes_.size());
-    fo->Write(dmlc::BeginPtr(stats_), sizeof(RTreeNodeStat) * nodes_.size());
-  }
+  void SaveModel(dmlc::Stream* fo) const override;
 
   bool operator==(const RegTree& b) const {
     return nodes_ == b.nodes_ && stats_ == b.stats_ &&