CRTP Inheritance Question

sandbox/feature_conversion.cc

@@ -0,0 +1,82 @@
+#include <iostream>
+
+namespace albatross {
+
+struct X {int value;};
+struct Y {int value;};
+
+template <typename ModelType> class ModelBase {
+private:
+  // This is nice to have because it makes sure you don't
+  // accidentally do something like:
+  //     class A : public ModelBase<B>
+  ModelBase() {};
+  friend ModelType;
+
+public:
+
+  template <typename FeatureType>
+  typename std::enable_if<has_possible_fit_impl<ModelType, FeatureType>::value, void>::type
+  fit(const FeatureType &feature) {
+    derived().fit_(feature);
+  }
+
+  /*
+   * CRTP Helpers
+   */
+  ModelType &derived() { return *static_cast<ModelType *>(this); }
+  const ModelType &derived() const {
+    return *static_cast<const ModelType *>(this);
+  }
+};
+
+void middle_fit(const X feature) {
+  std::cout << "middle_fit(X) : " << feature.value << std::endl;
+}
+
+class Middle {
+public:
+
+  void fit_(const X &feature) {
+    std::cout << "Middle.fit_(X) : " << feature.value << std::endl;
+  }
+
+};
+
+class Adapted : public ModelBase<Adapted> {
+public:
+
+  void fit_(const X &feature) {
+    std::cout << "Adapted.fit_(X) : " << feature.value << std::endl;
+    middle_fit(feature);
+  }
+
+  X convert_feature(const Y &y) {
+    return {y.value};
+  }
+
+  void fit_(const Y &feature) {
+    std::cout << "Adapted.fit_(Y) : " << feature.value << std::endl;
+    fit_(convert_feature(feature));
+  }
+
+};
+
+}
+
+int main()
+{
+  using namespace albatross;
+
+  Adapted m;
+
+  X x = {1};
+  m.fit(x);
+
+  Y y = {2};
+  m.fit(y);
+  // I'd really like to be able to do:
+  //  m.fit(y);
+
+  return 0;
+}