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diff --git a/meowpp/utility/state.h b/meowpp/utility/state.h
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+/*!
+ * @file state.h
+ * @brief Contains a base class for a state (in meowpp, most of all the return
+ *     value of a function (or to say, an "operation") will be a state).
+ *
+ * @author cathook
+ */
+
+#ifndef __MEOWPP_UTILITY_STATE_H__
+#define __MEOWPP_UTILITY_STATE_H__
+
+#include "object.h"
+
+namespace meow {
+
+
+/*!
+ * @brief The base class for state.
+ *
+ * Some example code:
+ * @code{.cpp}
+ * #include <meowpp/utility/state.h>
+ * #include <cstdio>
+ *
+ * using namespace meow;
+ *
+ * class Func1State : public State {
+ *  public:
+ *   static const int SAME = 0;
+ *   static const int DIFF = 1;
+ * };
+ *
+ * State Func1(int a, int b) {
+ *   if (a == b) {
+ *     return Func1State::SAME;
+ *   } else {
+ *     return Func1State::DIFF;
+ *   }
+ * }
+ *
+ * int main() {
+ *   if (Func1(3, 5) == Func1State::SAME) {
+ *     printf("same!\n");
+ *   } else {
+ *     printf("diff\n");
+ *   }
+ *   return 0;
+ * }
+ * @endcode
+ */
+class State : public Object {
+ private:
+  int value_;  //!< Stores the current state.
+
+ public:
+
+  /*!
+   * @brief Default constructor.
+   */
+  State() {}
+
+  /*!
+   * @brief Copy constructor.
+   */
+  State(State const& arg_another_state) : State(arg_another_state.value_) {}
+
+  /*!
+   * @brief Constructor.
+   */
+  State(int arg_init_value) : value_(arg_init_value) {}
+
+  /*!
+   * @brief Virtual destructor.
+   */
+  virtual ~State() {}
+
+  /*!
+   * @brief Gets the integer value of the state.
+   */
+  operator int() const {
+    return value_;
+  }
+
+  /*!
+   * @brief Sets the integer value of the state.
+   */
+  State& operator=(State const& arg_new_state) {
+    value_ = arg_new_state.value_;
+    return *this;
+  }
+
+  Object* Copy() const {
+    return new State(value_);
+  }
+
+  Object* CopyFrom(Object const* another_state) {
+    value_ = dynamic_cast<State const*>(another_state)->value_;
+    return this;
+  }
+  
+  bool Equals(Object const* another_state) {
+    return (value_ == dynamic_cast<State const*>(another_state)->value_);
+  }
+};
+
+}  // meow
+
+#endif  // __MEOWPP_UTILITY_STATE_H__