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variant: add mutable unwrap and visitation
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2 changed files with 41 additions and 9 deletions
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@ -62,7 +62,6 @@ namespace tools
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////
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////
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// variant: convenience wrapper around boost::variant with a cleaner interface
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// variant: convenience wrapper around boost::variant with a cleaner interface
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// - the value may be assigned to but is otherwise read-only
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// - the variant is 'optional' - an empty variant will evaluate to 'false' and an initialized variant will be 'true'
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// - the variant is 'optional' - an empty variant will evaluate to 'false' and an initialized variant will be 'true'
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///
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///
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template <typename ResultT>
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template <typename ResultT>
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@ -70,6 +69,7 @@ struct variant_static_visitor : public boost::static_visitor<ResultT>
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{
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{
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/// provide visitation for empty variants
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/// provide visitation for empty variants
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/// - add this to your visitor with: using variant_static_visitor::operator();
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/// - add this to your visitor with: using variant_static_visitor::operator();
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[[noreturn]] ResultT operator()(const boost::blank) { variant_static_visitor_blank_err(); }
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[[noreturn]] ResultT operator()(const boost::blank) const { variant_static_visitor_blank_err(); }
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[[noreturn]] ResultT operator()(const boost::blank) const { variant_static_visitor_blank_err(); }
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};
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};
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@ -107,14 +107,20 @@ public:
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template <typename T>
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template <typename T>
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bool is_type() const noexcept { return this->index() == this->type_index_of<T>(); }
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bool is_type() const noexcept { return this->index() == this->type_index_of<T>(); }
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/// try to get a read-only handle to the embedded value (return nullptr on failure)
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/// try to get a handle to the embedded value (return nullptr on failure)
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template <typename T>
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template <typename T>
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const T* try_unwrap() const
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T* try_unwrap() noexcept { return boost::strict_get< T>(&m_value); }
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{
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template <typename T>
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return boost::strict_get<T>(&m_value);
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const T* try_unwrap() const noexcept { return boost::strict_get<const T>(&m_value); }
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}
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/// get a read-only handle to the embedded value
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/// get a handle to the embedded value
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template <typename T>
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T& unwrap()
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{
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T *value_ptr{this->try_unwrap<T>()};
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if (!value_ptr) variant_unwrap_err();
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return *value_ptr;
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}
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template <typename T>
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template <typename T>
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const T& unwrap() const
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const T& unwrap() const
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{
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{
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@ -131,7 +137,7 @@ public:
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static constexpr int type_index_of() noexcept
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static constexpr int type_index_of() noexcept
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{
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{
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using types = boost::mpl::vector<boost::blank, Types...>;
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using types = boost::mpl::vector<boost::blank, Types...>;
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using elem = typename boost::mpl::find<types, T>::type;
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using elem = typename boost::mpl::find<types, T>::type;
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using begin = typename boost::mpl::begin<types>::type;
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using begin = typename boost::mpl::begin<types>::type;
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return boost::mpl::distance<begin, elem>::value;
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return boost::mpl::distance<begin, elem>::value;
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}
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}
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@ -142,6 +148,11 @@ public:
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/// apply a visitor to the variant
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/// apply a visitor to the variant
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template <typename VisitorT>
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template <typename VisitorT>
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typename VisitorT::result_type visit(VisitorT &&visitor)
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{
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return boost::apply_visitor(std::forward<VisitorT>(visitor), m_value);
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}
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template <typename VisitorT>
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typename VisitorT::result_type visit(VisitorT &&visitor) const
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typename VisitorT::result_type visit(VisitorT &&visitor) const
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{
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{
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return boost::apply_visitor(std::forward<VisitorT>(visitor), m_value);
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return boost::apply_visitor(std::forward<VisitorT>(visitor), m_value);
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@ -232,8 +232,10 @@ struct test_stringify_visitor: public variant_static_visitor<std::string>
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return test_stringify_visitor::stringify(t);
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return test_stringify_visitor::stringify(t);
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}
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}
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};
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};
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} // anonymous namespace
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//-------------------------------------------------------------------------------------------------------------------
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//-------------------------------------------------------------------------------------------------------------------
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//-------------------------------------------------------------------------------------------------------------------
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} // anonymous namespace
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//-------------------------------------------------------------------------------------------------------------------
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//-------------------------------------------------------------------------------------------------------------------
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TEST(variant, operatorbool)
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TEST(variant, operatorbool)
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{
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{
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@ -295,6 +297,25 @@ TEST(variant, unwrap)
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EXPECT_THROW(v.unwrap<std::string>(), std::runtime_error);
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EXPECT_THROW(v.unwrap<std::string>(), std::runtime_error);
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}
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}
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//-------------------------------------------------------------------------------------------------------------------
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//-------------------------------------------------------------------------------------------------------------------
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TEST(variant, mutation)
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{
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variant<uint8_t> v;
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v = (uint8_t) 5;
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EXPECT_EQ(5, v.unwrap<uint8_t>());
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uint8_t &intref{v.unwrap<uint8_t>()};
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intref = 10;
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EXPECT_EQ(10, v.unwrap<uint8_t>());
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EXPECT_TRUE(v.try_unwrap<uint8_t>());
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uint8_t *intptr{v.try_unwrap<uint8_t>()};
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*intptr = 15;
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EXPECT_EQ(15, v.unwrap<uint8_t>());
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const variant<uint8_t> &v_ref{v};
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EXPECT_EQ(15, v_ref.unwrap<uint8_t>());
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EXPECT_TRUE(v_ref.try_unwrap<uint8_t>());
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EXPECT_EQ(15, *(v_ref.try_unwrap<uint8_t>()));
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}
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//-------------------------------------------------------------------------------------------------------------------
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TEST(variant, index)
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TEST(variant, index)
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{
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{
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variant<int8_t, uint8_t, int16_t, uint16_t, std::string> v;
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variant<int8_t, uint8_t, int16_t, uint16_t, std::string> v;
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