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162 lines
5.1 KiB
Plaintext
162 lines
5.1 KiB
Plaintext
optional
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A class where the value is optional.
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If a value is not assigned then an object of the contained type is not constructed.
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etl::optional<T>
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If _DEBUG is defined then accesses to invalid data is detected either by throwing (ETL_THROW_EXCEPTIONS defined) or calling the error handler.
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____________________________________________________________________________________________________
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Template deduction guides
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C++17 and above
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template <typename T>
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etl::optional(T)
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-> etl::optional<T>;
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Example
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std::string text = "Hello";
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etl::optional opt{ text };
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Defines opt as containing a std::string, containing the supplied text.
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Constructor
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optional()
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Default constructor.
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optional(const T& value)
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optional(T&& value)
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Construct from value. Constructs a T.
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____________________________________________________________________________________________________
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optional(const optional<T>& other)
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optional(optional<T>&& other)
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Construct copy. Constructs a T.
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optional(nullopt)
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Construct empty value (same as default constructor).
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template <typename... TArgs>
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ETL_CONSTEXPR14
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optional_impl(etl::in_place_t, TArgs&&... args)
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Constructor from variadic args.
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20.43.0
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____________________________________________________________________________________________________
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template <typename U, typename... TArgs>
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ETL_CONSTEXPR14
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optional_impl(etl::in_place_t, std::initializer_list<U> ilist, TArgs&&... args)
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Constructor from variadic args.
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20.43.0
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____________________________________________________________________________________________________
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~optional()
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Destructor. Destructs a T if a value has been assigned.
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Operations
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optional& operator =(etl::nullopt)
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optional& operator =(const optional<T>& value)
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optional& operator =(optional<T>&& value)
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optional& operator =(const T& value)
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optional& operator =(T&& value)
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Note:
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Unlike std::optional, assigning from { } will not clear the optional item to 'empty'.
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It will be assigned a default constructed 'value'.
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etl::optional<int> opt;
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opt = { }; // opt will contain 0.
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____________________________________________________________________________________________________
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void swap(optional& other)
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Swaps with the other optional
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void reset()
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Resets the optional back to default.
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C++03
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template <typename T1>
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void emplace(const T1& value1)
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template <typename T1, typename T2>
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void emplace(const T1& value1, const T2& value2)
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template <typename T1, typename T2, typename T3>
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void emplace(const T1& value1, const T2& value2, const T3& value3)
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template <typename T1, typename T2, typename T3, typename T4>
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void emplace(const T1& value1, const T2& value2, const T3& value3, const T4& value4)
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C++11
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template <typename ... Args>
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void emplace(Args && ... args)
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Observers
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const T& value() const
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T& value();
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Returns the contained value.
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____________________________________________________________________________________________________
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template <typename T >
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T value_or(T value) const
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template <typename T>
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T value_or(T value)
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Returns the contained value if *this is valid, otherwise returns value.
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const T* operator->() const
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T* operator->();
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Returns a pointer to the contained value.
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const T& operator *() const
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T* operator *();
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Returns a reference to the contained value.
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Tests
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explicit operator bool() const
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bool has_value() const
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Checks whether *this is in a valid state, i.e. whether the contained value is initialised.
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Returns true if valid, otherwise false.
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Non-member functions
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== true if the contents are equal, otherwise false.
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!= true if the contents are not equal, otherwise false.
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< true if the contents of the lhs are less than the contents of the rhs, otherwise false.
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<= true if the contents of the lhs are less than or equal to the contents of the rhs, otherwise false.
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> true if the contents of the lhs are greater than the contents of the rhs, otherwise false.
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>= true if the contents of the lhs are greater than or equal to the contents of the rhs, otherwise false.
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