| Line | Branch | Exec | Source |
|---|---|---|---|
| 1 | // See [What is “virtual data,” and how-can / why-would I use it in C++?] | ||
| 2 | // (https://isocpp.org/wiki/faq/value-vs-ref-semantics#virt-data) | ||
| 3 | |||
| 4 | #include "StretchableArray.hpp" | ||
| 5 | #include "Verbose.hpp" | ||
| 6 | #include <functional> | ||
| 7 | #include <iostream> | ||
| 8 | |||
| 9 | class StackRef { | ||
| 10 | public: | ||
| 11 | void Push(double x); | ||
| 12 | double Pop(); | ||
| 13 | |||
| 14 | protected: | ||
| 15 | // The base class has no public constructor and does not provide its own | ||
| 16 | // object. Instead it accepts an object from a derived class. | ||
| 17 | StackRef(Array& data); | ||
| 18 | |||
| 19 | private: | ||
| 20 | // To simulate virtual data in C++, the base class has a reference to the | ||
| 21 | // member object and the derived class’s destructor deletes the object. | ||
| 22 | // No additional memory allocation overhead is imposed, | ||
| 23 | // but copy assignment becomes impossible. | ||
| 24 | std::reference_wrapper<Array> data_; | ||
| 25 | gsl::index index_{0}; | ||
| 26 | }; | ||
| 27 | |||
| 28 | //////////////////////////////////////////////////////////////////////////////// | ||
| 29 | |||
| 30 | // Virtual data makes the implementation of the derived class easier: | ||
| 31 | // most of the implementation is inherited. | ||
| 32 | class FixedStackRef : public StackRef { | ||
| 33 | public: | ||
| 34 | // The derived class has a constructor that provides an object to the base class. | ||
| 35 | explicit FixedStackRef(gsl::index size = 1); | ||
| 36 | |||
| 37 | private: | ||
| 38 | // The derived class contains the member object. | ||
| 39 | Array value_; | ||
| 40 | }; | ||
| 41 | |||
| 42 | //////////////////////////////////////////////////////////////////////////////// | ||
| 43 | |||
| 44 | // Virtual data makes the implementation of the derived class easier: | ||
| 45 | // most of the implementation is inherited. | ||
| 46 | class StretchableStackRef : public StackRef { | ||
| 47 | public: | ||
| 48 | // The derived class has a constructor that provides an object to the base class. | ||
| 49 | explicit StretchableStackRef(gsl::index size = 1); | ||
| 50 | |||
| 51 | private: | ||
| 52 | // The derived class contains the member object. | ||
| 53 | StretchableArray value_; | ||
| 54 | }; | ||
| 55 | |||
| 56 | //////////////////////////////////////////////////////////////////////////////// | ||
| 57 | |||
| 58 | 4 | StackRef::StackRef(Array& data) : data_{data} { | |
| 59 | 4 | std::cout << gsl::czstring{__func__} << ": &data_=" << &data_.get() | |
| 60 | 4 | << std::endl; | |
| 61 | 4 | } | |
| 62 | |||
| 63 | 11 | void StackRef::Push(double x) { | |
| 64 | 11 | data_.get()[index_++] = x; // may throw | |
| 65 | 10 | } | |
| 66 | |||
| 67 | 8 | double StackRef::Pop() { | |
| 68 | 8 | return data_.get()[--index_]; // may throw | |
| 69 | } | ||
| 70 | |||
| 71 | //////////////////////////////////////////////////////////////////////////////// | ||
| 72 | |||
| 73 | 3 | FixedStackRef::FixedStackRef(gsl::index size) : StackRef{value_}, value_{size} { | |
| 74 |
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3 | std::cout << gsl::czstring{__func__} << ": &value_=" << &value_ << std::endl; |
| 75 | 3 | } | |
| 76 | |||
| 77 | //////////////////////////////////////////////////////////////////////////////// | ||
| 78 | |||
| 79 | 1 | StretchableStackRef::StretchableStackRef(gsl::index size) : | |
| 80 | 1 | StackRef{value_}, value_{size} { | |
| 81 |
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1 | std::cout << gsl::czstring{__func__} << ": &value_=" << &value_ << std::endl; |
| 82 | 1 | } | |
| 83 | |||
| 84 | //////////////////////////////////////////////////////////////////////////////// | ||
| 85 | |||
| 86 | #include <gtest/gtest.h> | ||
| 87 | |||
| 88 | 8 | TEST(VirtualDataRef, Stack_Push_Pop) { | |
| 89 | 2 | const auto size = gsl::index{3}; | |
| 90 |
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6 | auto stack = Verbose<FixedStackRef>{"stack", size}; |
| 91 |
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8 | for (auto x = gsl::index{0}; x < size; x++) { |
| 92 |
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6 | stack.Push(gsl::narrow_cast<double>(x)); |
| 93 | } | ||
| 94 |
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8 | for (auto x = size - 1; x >= 0; x--) { |
| 95 |
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6 | EXPECT_EQ(gsl::narrow_cast<double>(x), stack.Pop()); |
| 96 | } | ||
| 97 | 4 | } | |
| 98 | |||
| 99 | 8 | TEST(VirtualDataRef, Stack_Push_Full) { | |
| 100 | 2 | auto size = gsl::index{3}; | |
| 101 |
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6 | auto stack = Verbose<FixedStackRef>{"stack", size}; |
| 102 |
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8 | for (auto x = gsl::index{0}; x < size; x++) { |
| 103 |
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6 | stack.Push(gsl::narrow_cast<double>(x)); |
| 104 | } | ||
| 105 |
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2 | EXPECT_THROW(stack.Push(gsl::narrow_cast<double>(size)), std::out_of_range); |
| 106 | 4 | } | |
| 107 | |||
| 108 | 8 | TEST(VirtualDataRef, Stack_Pop_Empty) { | |
| 109 |
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6 | auto stack = Verbose<FixedStackRef>{"stack", 1}; |
| 110 |
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2 | EXPECT_THROW(stack.Pop(), std::out_of_range); |
| 111 | 4 | } | |
| 112 | |||
| 113 | 8 | TEST(VirtualDataRef, Stack_Stretch) { | |
| 114 | 2 | const auto size = gsl::index{3}; | |
| 115 |
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6 | auto stack = Verbose<StretchableStackRef>{"stack", size}; |
| 116 |
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8 | for (auto x = gsl::index{0}; x < size; x++) { |
| 117 |
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6 | stack.Push(gsl::narrow_cast<double>(x)); |
| 118 | } | ||
| 119 |
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2 | EXPECT_NO_THROW(stack.Push(gsl::narrow_cast<double>(size))); |
| 120 |
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2 | EXPECT_EQ(gsl::narrow_cast<double>(size), stack.Pop()); |
| 121 |
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8 | for (auto x = size - 1; x >= 0; x--) { |
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6 | EXPECT_EQ(gsl::narrow_cast<double>(x), stack.Pop()); |
| 123 | } | ||
| 124 | 4 | } | |
| 125 |