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src/sql/engine/expr/ob_const_map_initializer.h

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+/**
+ * Copyright (c) 2021 OceanBase
+ * OceanBase CE is licensed under Mulan PubL v2.
+ * You can use this software according to the terms and conditions of the Mulan PubL v2.
+ * You may obtain a copy of Mulan PubL v2 at:
+ *          http://license.coscl.org.cn/MulanPubL-2.0
+ * THIS SOFTWARE IS PROVIDED ON AN "AS IS" BASIS, WITHOUT WARRANTIES OF ANY KIND,
+ * EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO NON-INFRINGEMENT,
+ * MERCHANTABILITY OR FIT FOR A PARTICULAR PURPOSE.
+ * See the Mulan PubL v2 for more details.
+ */
+
+#ifndef _OB_CONST_MAP_INITIALIZER_H
+#define _OB_CONST_MAP_INITIALIZER_H
+
+#include "lib/ob_errno.h"
+#include "lib/utility/utility.h"
+
+namespace oceanbase {
+namespace sql {
+
+/**
+ * a defined static const map value of class MyClass
+ * usually needs to be inited when declearing it
+ * ObConstMap helps in this situatition using
+ * a init_function
+ *
+ */
+
+template <typename MyClass>
+class ObConstMap {
+  public:
+  typedef int (*InitFunction)(MyClass& member);
+
+  explicit ObConstMap(InitFunction init_f) : is_inited_(false), init_f_(init_f)
+  {}
+
+  int init()
+  {
+    int ret = common::OB_SUCCESS;
+    if (OB_UNLIKELY(is_inited_)) {
+      ret = common::OB_INIT_TWICE;
+    } else {
+      is_inited_ = true;
+      ret = init_f_(member_);
+    }
+    return ret;
+  }
+
+  const MyClass& value()
+  {
+    return member_;
+  }
+
+  protected:
+  bool is_inited_;
+  InitFunction init_f_;
+  MyClass member_;
+};
+
+}  // namespace sql
+
+}  // namespace oceanbase
+
+#endif  // _OB_CONST_MAP_INITIALIZER_H