1 /*
2  *  Copyright (c) 2020, The OpenThread Authors.
3  *  All rights reserved.
4  *
5  *  Redistribution and use in source and binary forms, with or without
6  *  modification, are permitted provided that the following conditions are met:
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8  *     notice, this list of conditions and the following disclaimer.
9  *  2. Redistributions in binary form must reproduce the above copyright
10  *     notice, this list of conditions and the following disclaimer in the
11  *     documentation and/or other materials provided with the distribution.
12  *  3. Neither the name of the copyright holder nor the
13  *     names of its contributors may be used to endorse or promote products
14  *     derived from this software without specific prior written permission.
15  *
16  *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
17  *  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18  *  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19  *  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
20  *  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
21  *  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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23  *  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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25  *  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
26  *  POSSIBILITY OF SUCH DAMAGE.
27  */
28 
29 /**
30  * @file
31  *   This file includes type traits definitions.
32  */
33 
34 #ifndef OT_TYPE_TRAITS_HPP_
35 #define OT_TYPE_TRAITS_HPP_
36 
37 namespace ot {
38 namespace TypeTraits {
39 
40 /**
41  * Represents a true value (contains a `true` static `kValue` member variable).
42  *
43  */
44 struct TrueValue
45 {
46     constexpr static bool kValue = true; ///< true value.
47 };
48 
49 /**
50  * Represents a false value (contains a `false` static `kValue` member variable).
51  *
52  */
53 struct FalseValue
54 {
55     constexpr static bool kValue = false; ///< false value.
56 };
57 
58 /**
59  * Indicates whether or not a given template `Type` is a pointer type.
60  *
61  * The `constexpr` expression `IsPointer<Type>::kValue` would be `true` when the `Type` is a pointer, otherwise it
62  * would be `false`.
63  *
64  * @tparam Type    A type to check if is a pointer.
65  *
66  */
67 template <typename Type> struct IsPointer : public FalseValue
68 {
69 };
70 
71 // Partial template specializations of the `IsPointer<Type>`
72 
73 template <typename Type> struct IsPointer<Type *> : public TrueValue
74 {
75 };
76 
77 template <typename Type> struct IsPointer<const Type *> : public TrueValue
78 {
79 };
80 
81 template <typename Type> struct IsPointer<volatile Type *> : public TrueValue
82 {
83 };
84 
85 template <typename Type> struct IsPointer<const volatile Type *> : TrueValue
86 {
87 };
88 
89 /**
90  * Indicates whether or not a given template `FirstType is the same as `SecondType`.
91  *
92  * The `constexpr` expression `IsSame<FirstType, SecondType>::kValue` would be `true` when the two types are the same,
93  * otherwise it would be `false`.
94  *
95  * @tparam FirstType     The first type.
96  * @tparam SecondType    The second type.
97  *
98  */
99 template <typename FirstType, typename SecondType> struct IsSame : public FalseValue
100 {
101 };
102 
103 template <typename Type> struct IsSame<Type, Type> : public TrueValue
104 {
105 };
106 
107 /**
108  * Selects between two given types based on a boolean condition at compile time.
109  *
110  * It provides member type named `Type` which is defined as `TypeOnTrue` if `kCondition` is `true` at compile time, or
111  * as `TypeOnFalse` if `kCondition` is `false`.
112  *
113  * @tparam kCondition   The boolean condition which is used to select between the two types.
114  * @tparam TypeOnTrue   The type to select when `kCondition` is `true`.
115  * @tparam TypeOnFalse  The type to select when `kCondition` is `false`.
116  *
117  */
118 template <bool kCondition, typename TypeOnTrue, typename TypeOnFalse> struct Conditional
119 {
120     typedef TypeOnFalse Type; ///< The selected type based on `kCondition`.
121 };
122 
123 template <typename TypeOnTrue, typename TypeOnFalse> struct Conditional<true, TypeOnTrue, TypeOnFalse>
124 {
125     typedef TypeOnTrue Type;
126 };
127 
128 /**
129  * Determines the return type of a given function pointer type.
130  *
131  * It provides member type named `Type` which gives the return type of `HandlerType` function pointer.
132  *
133  * For example, `ReturnTypeOf<Error (*)(void *aContext)>::Type` would be `Error`.
134  *
135  * @tparam HandlerType   The function pointer type.
136  *
137  */
138 template <typename HandlerType> struct ReturnTypeOf;
139 
140 template <typename RetType, typename... Args> struct ReturnTypeOf<RetType (*)(Args...)>
141 {
142     typedef RetType Type; ///< The return type.
143 };
144 
145 /**
146  * Determines the type of the first argument of a given function pointer type.
147  *
148  * It provides member type named `Type` which gives the first argument type of `HandlerType` function pointer.
149  *
150  * For example, `ReturnTypeOf<Error (*)(void *aContext)>::Type` would be `void *`.
151  *
152  * @tparam HandlerType   The function pointer type.
153  *
154  */
155 template <typename HandlerType> struct FirstArgTypeOf;
156 
157 template <typename RetType, typename FirstArgType, typename... Args>
158 struct FirstArgTypeOf<RetType (*)(FirstArgType, Args...)>
159 {
160     typedef FirstArgType Type; ///< The first argument type.
161 };
162 
163 } // namespace TypeTraits
164 } // namespace ot
165 
166 #endif // OT_TYPE_TRAITS_HPP_
167