[ShogunBoard] Add parameter observable and observe_scalar() method.

subscribe_to_parameters() is still empty because we need to know
how ParameterObserver will be implemented.

observe_scalar() takes now a pair <string, Any>, which are the name
of the observed parameter and the value (type erased) of the
parameter.

src/shogun/base/SGObject.cpp

@@ -150,7 +150,10 @@ namespace shogun
 
 using namespace shogun;
 
-CSGObject::CSGObject() : self()
+CSGObject::CSGObject()
+    : self(), m_subject_params(),
+      m_observable_params(m_subject_params.get_observable()),
+      m_subscriber_params(m_subject_params.get_subscriber())
 {
 	init();
 	set_global_objects();
@@ -160,7 +163,10 @@ CSGObject::CSGObject() : self()
 }
 
 CSGObject::CSGObject(const CSGObject& orig)
-: self(), io(orig.io), parallel(orig.parallel), version(orig.version)
+    : self(), io(orig.io), parallel(orig.parallel), version(orig.version),
+      m_subject_params(orig.m_subject_params),
+      m_observable_params(orig.m_observable_params),
+      m_subscriber_params(orig.m_subscriber_params)
 {
 	init();
 	set_global_objects();
@@ -753,7 +759,7 @@ bool CSGObject::clone_parameters(CSGObject* other)
 {
 	REQUIRE(other, "Provided instance must be non-empty.\n");
 	index_t num_parameters = m_parameters->get_num_parameters();
-	
+
 	REQUIRE(other->m_parameters->get_num_parameters() == num_parameters,
 		"Number of parameters of provided instance (%d) must match this instance (%d).\n",
 		other->m_parameters->get_num_parameters(), num_parameters);
@@ -800,3 +806,8 @@ bool CSGObject::type_erased_has(const BaseTag& _tag) const
 {
 	return self->has(_tag);
 }
+
+void CSGObject::observe_scalar(const std::string& name, const Any& value)
+{
+	m_subscriber_params.on_next(std::make_pair(name, value));
+}

src/shogun/base/SGObject.h

@@ -23,6 +23,9 @@
 #include <shogun/lib/tag.h>
 #include <shogun/lib/any.h>
 
+#include <rxcpp/rx.hpp>
+#include <utility>
+
 /** \namespace shogun
  * @brief all of classes and functions are contained in the shogun namespace
  */
@@ -394,6 +397,22 @@ class CSGObject
 		return get(tag);
 	}
 
+#ifndef SWIG
+	/**
+	  * Get parameters observable
+	  * @return RxCpp observable
+	  */
+	rxcpp::observable<std::pair<std::string, Any>> get_parameters_observable()
+	{
+		return m_observable_params;
+	};
+#endif
+
+	/** Subscribe a parameter observer to watch over params */
+	void subscribe_to_parameters()
+	{
+	}
+
 protected:
 	/** Can (optionally) be overridden to pre-initialize some member
 	 *  variables which are not PARAMETER::ADD'ed.  Make sure that at
@@ -545,6 +564,12 @@ class CSGObject
 	class Self;
 	Unique<Self> self;
 
+protected:
+	/** Observe the parameter and emits a value using the
+	* observable object
+	*/
+	void observe_scalar(const std::string& name, const Any& value);
+
 public:
 	/** io */
 	SGIO* io;
@@ -576,6 +601,15 @@ class CSGObject
 	bool m_save_post_called;
 
 	RefCount* m_refcount;
+
+	/** Subject used to create the params observer */
+	rxcpp::subjects::subject<std::pair<std::string, Any>> m_subject_params;
+
+	/** Parameter Observable */
+	rxcpp::observable<std::pair<std::string, Any>> m_observable_params;
+
+	/** Subscriber used to call onNext, onComplete etc.*/
+	rxcpp::subscriber<std::pair<std::string, Any>> m_subscriber_params;
 };
 }
 #endif // __SGOBJECT_H__