1 /*
2  * Copyright (C) 2015 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 ART_CMDLINE_DETAIL_CMDLINE_PARSER_DETAIL_H_
18 #define ART_CMDLINE_DETAIL_CMDLINE_PARSER_DETAIL_H_
19 
20 #include <string>
21 #include <sstream>
22 #include <vector>
23 
24 namespace art {
25   // Implementation details for some template querying. Don't look inside if you hate templates.
26   namespace detail {
27     template <typename T>
28     typename std::remove_reference<T>::type& FakeReference();
29 
30     // SupportsInsertionOperator<T, TStream>::value will evaluate to a boolean,
31     // whose value is true if the TStream class supports the << operator against T,
32     // and false otherwise.
33     template <typename T2, typename TStream2 = std::ostream>
34     struct SupportsInsertionOperator {
35      private:
36       template <typename TStream, typename T>
37       static std::true_type InsertionOperatorTest(TStream& os, const T& value,
38                                                   std::remove_reference<decltype(os << value)>* = 0); // NOLINT [whitespace/operators] [3]
39 
40       template <typename TStream, typename ... T>
41       static std::false_type InsertionOperatorTest(TStream& os, const T& ... args);
42 
43      public:
44       static constexpr bool value =
45           decltype(InsertionOperatorTest(FakeReference<TStream2>(), std::declval<T2>()))::value;
46     };
47 
48     template <typename TLeft, typename TRight = TLeft, bool IsFloatingPoint = false>
49     struct SupportsEqualityOperatorImpl;
50 
51     template <typename TLeft, typename TRight>
52     struct SupportsEqualityOperatorImpl<TLeft, TRight, false> {
53      private:
54       template <typename TL, typename TR>
55       static std::true_type EqualityOperatorTest(const TL& left, const TR& right,
56                                                  std::remove_reference<decltype(left == right)>* = 0); // NOLINT [whitespace/operators] [3]
57 
58       template <typename TL, typename ... T>
59       static std::false_type EqualityOperatorTest(const TL& left, const T& ... args);
60 
61      public:
62       static constexpr bool value =
63           decltype(EqualityOperatorTest(std::declval<TLeft>(), std::declval<TRight>()))::value;
64     };
65 
66     // Partial specialization when TLeft/TRight are both floating points.
67     // This is a work-around because decltype(floatvar1 == floatvar2)
68     // will not compile with clang:
69     // error: comparing floating point with == or != is unsafe [-Werror,-Wfloat-equal]
70     template <typename TLeft, typename TRight>
71     struct SupportsEqualityOperatorImpl<TLeft, TRight, true> {
72       static constexpr bool value = true;
73     };
74 
75     // SupportsEqualityOperatorImpl<T1, T2>::value will evaluate to a boolean,
76     // whose value is true if T1 can be compared against T2 with ==,
77     // and false otherwise.
78     template <typename TLeft, typename TRight = TLeft>
79     struct SupportsEqualityOperator :
80         SupportsEqualityOperatorImpl<TLeft, TRight,
81                                      std::is_floating_point<TLeft>::value
82                                      && std::is_floating_point<TRight>::value> {
83     };
84 
85     // Convert any kind of type to an std::string, even if there's no
86     // serialization support for it. Unknown types get converted to an
87     // an arbitrary value.
88     //
89     // Meant for printing user-visible errors or unit test failures only.
90     template <typename T>
91     std::string ToStringAny(const T& value,
92                             typename std::enable_if<
93                                 SupportsInsertionOperator<T>::value>::type* = 0) {
94       std::stringstream stream;
95       stream << value;
96       return stream.str();
97     }
98 
99     template <typename T>
100     std::string ToStringAny(const std::vector<T> value,
101                             typename std::enable_if<
102                                 SupportsInsertionOperator<T>::value>::type* = 0) {
103       std::stringstream stream;
104       stream << "vector{";
105 
106       for (size_t i = 0; i < value.size(); ++i) {
107         stream << ToStringAny(value[i]);
108 
109         if (i != value.size() - 1) {
110           stream << ',';
111         }
112       }
113 
114       stream << "}";
115       return stream.str();
116     }
117 
118     template <typename T>
119     std::string ToStringAny(const T&,
120                             typename std::enable_if<
121                                 !SupportsInsertionOperator<T>::value>::type* = 0
122     ) {
123       return std::string("(unknown type [no operator<< implemented] for )");
124     }
125   }  // namespace detail  // NOLINT [readability/namespace] [5]
126 }  // namespace art
127 
128 #endif  // ART_CMDLINE_DETAIL_CMDLINE_PARSER_DETAIL_H_
129