1 /*
2  * Copyright (C) 2016 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 #ifndef TRUSTY_NVRAM_OPTIONAL_H_
18 #define TRUSTY_NVRAM_OPTIONAL_H_
19 
20 namespace nvram {
21 
22 // A generic option type. In addition to the underlying value, it holds a flag
23 // indicating whether the value is valid.
24 template <typename ValueType> class Optional {
25  public:
26   Optional() = default;
Optional(ValueType value)27   explicit Optional(ValueType value) : value_(value), valid_(true) {}
28 
valid()29   bool valid() const { return valid_; }
value()30   const ValueType& value() const { return value_; }
31 
32   // Mark the object as valid and return a reference to the wrapped value.
Activate()33   ValueType& Activate() {
34     valid_ = true;
35     value_ = ValueType{};
36     return value_;
37   }
38 
39   // Mark the object as invalid.
Clear()40   void Clear() {
41     valid_ = false;
42   }
43 
44  private:
45   ValueType value_{};
46   bool valid_ = false;
47 };
48 
49 }  // namespace nvram
50 
51 #endif  // TRUSTY_NVRAM_OPTIONAL_H_
52