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 <sstream>
21 #include <string>
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 :  // NOLINT [whitespace/labels] [4]
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