Add wrapper for class member function references.

lib/pls/include/pls/internal/helpers/member_function.h

+
+#ifndef PLS_INTERNAL_HELPERS_MEMBER_FUNCTION_H_
+#define PLS_INTERNAL_HELPERS_MEMBER_FUNCTION_H_
+
+namespace pls {
+namespace internal {
+namespace helpers {
+
+template<class C, typename R, typename ...ARGS>
+class member_function {
+ public:
+  using type = member_function<C, R, ARGS...>;
+
+  member_function(C *object, R (C::*function_pointer)(ARGS...)) : object_{object},
+                                                                  function_pointer_{function_pointer} {}
+
+  R operator()(ARGS... args) {
+    ((*object_).*function_pointer_)(args...);
+  }
+
+ private:
+  C *object_;
+  R (C::*function_pointer_)(ARGS...);
+};
+
+template<typename C, typename R, typename ...ARGS>
+static constexpr member_function<C, R, ARGS...> bind(C *object, R (C::*function_pointer)(ARGS...)) {
+  return {object, function_pointer};
+}
+
+}
+}
+}
+
+#endif //PLS_INTERNAL_HELPERS_MEMBER_FUNCTION_H_