fable: Fix un-reusable interface of Factory class

Also remove factory.hpp from set of headers in schema.hpp,
since most users of the library don't need Factory by default.
Those who want to use it need to include it explicitely now.

Add add_default_factory method to Factory schema.

Add args subset option to Factory schema.

Add schema transform method to Factory schema.

Author: cassava

engine/src/stack.hpp

@@ -39,6 +39,7 @@
 #include <cloe/simulator.hpp>        // for SimulatorFactory
 #include <cloe/trigger.hpp>          // for Source
 #include <cloe/utility/command.hpp>  // for Command
+#include <fable/schema/factory.hpp>  // for Factory
 
 #include "plugin.hpp"  // for Plugin
 

fable/CMakeLists.txt

@@ -51,6 +51,8 @@ if(BuildTests)
         src/fable/environment_test.cpp
         src/fable/schema/const_test.cpp
         src/fable/schema/enum_test.cpp
+        src/fable/schema/factory_test.cpp
+        src/fable/schema/factory_advanced_test.cpp
         src/fable/schema/number_test.cpp
         src/fable/schema/optional_test.cpp
         src/fable/schema/struct_test.cpp

fable/include/fable/schema.hpp

@@ -132,7 +132,6 @@
 #include <fable/schema/const.hpp>      // for Const<>
 #include <fable/schema/duration.hpp>   // for Duration<>
 #include <fable/schema/enum.hpp>       // for Enum<>
-#include <fable/schema/factory.hpp>    // for Factory<>
 #include <fable/schema/ignore.hpp>     // for Ignore
 #include <fable/schema/interface.hpp>  // for Interface, Box
 #include <fable/schema/json.hpp>       // for FromJson<>

fable/include/fable/schema/confable.hpp

@@ -45,19 +45,22 @@ class FromConfable : public Base<FromConfable<T>> {
   using Type = T;
 
   explicit FromConfable(std::string&& desc = "") {
-    schema_ = T().schema();
+    schema_ = Type().schema();
     schema_.reset_ptr();
     this->type_ = schema_.type();
     this->desc_ = std::move(desc);
   }
 
   FromConfable(Type* ptr, std::string&& desc)
-      : Base<FromConfable<T>>(ptr->schema().type(), std::move(desc))
+      : Base<FromConfable<Type>>(ptr->schema().type(), std::move(desc))
       , schema_(ptr->schema())
       , ptr_(ptr) {
     assert(ptr != nullptr);
   }
 
+ public:  // Special
+  Box get_confable_schema() const { return schema_.clone(); }
+
  public:  // Overrides
   Json json_schema() const override {
     Json j = schema_.json_schema();
@@ -86,7 +89,7 @@ class FromConfable : public Base<FromConfable<T>> {
   Json serialize(const Type& x) const { return x.to_json(); }
 
   Type deserialize(const Conf& c) const {
-    T tmp;
+    Type tmp;
     tmp.from_conf(c);
     return tmp;
   }