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| optional () |
| | constructs an object that does not contain a value.
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| optional (dmlc::nullopt_t) noexcept |
| | constructs an object that does contain a nullopt value.
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| optional (const optional< T > &other) |
| | construct an optional object with another optional object
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| optional (optional &&other) noexcept(std::is_nothrow_move_constructible< T >::value &&std::is_nothrow_move_assignable< T >::value) |
| | move constructor: If other contains a value, then stored value is direct-intialized with it.
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template<typename... Args> |
| | optional (enable_if_t< std::is_constructible< T, Args... >::value, in_place_t >, Args &&...args) |
| | constructs an optional object that contains a value, initialized as if direct-initializing
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template<typename U , typename... Args> |
| | optional (enable_if_t< std::is_constructible< T, std::initializer_list< U > &, Args &&... >::value, in_place_t >, std::initializer_list< U > ilist, Args &&...args) |
| | Constructs an optional object that contains a value, initialized as if direct-initializing.
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template<typename U = value_type, enable_if_t< std::is_convertible< U &&, T >::value > * = nullptr, enable_constructor_from_value< T, U > * = nullptr> |
| | optional (U &&other) noexcept |
| | constructs the stored value with value with other parameter.
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template<typename U = value_type, enable_if_t<!std::is_convertible< U &&, T >::value > * = nullptr, enable_constructor_from_value< T, U > * = nullptr> |
| | optional (U &&other) noexcept |
| | explicit constructor: constructs the stored value with other parameter.
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template<typename U , enable_constructor_from_other< T, U, const U & > * = nullptr, enable_if_t< std::is_convertible< const U &, T >::value > * = nullptr> |
| | optional (const optional< U > &other) |
| | converting copy constructor
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template<typename U , enable_constructor_from_other< T, U, const U & > * = nullptr, enable_if_t<!std::is_convertible< const U &, T >::value > * = nullptr> |
| | optional (const optional< U > &other) |
| | explicit converting copy constructor
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template<typename U , enable_constructor_from_other< T, U, U && > * = nullptr, enable_if_t< std::is_convertible< U &&, T >::value > * = nullptr> |
| | optional (optional< U > &&other) |
| | converting move constructor
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template<typename U , enable_constructor_from_other< T, U, U && > * = nullptr, enable_if_t<!std::is_convertible< U &&, T >::value > * = nullptr> |
| | optional (optional< U > &&other) |
| | explicit converting move constructor
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void | reset () noexcept |
| | reset
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| ~optional () |
| | deconstructor
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void | swap (optional< T > &other) |
| | swap two optional
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| optional< T > & | operator= (const T &value) |
| | set this object to hold value
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| optional< T > & | operator= (const optional< T > &other) |
| | set this object to hold the same value with other
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optional< T > & | operator= (nullopt_t) |
| | clear the value this object is holding. optional<T> x = nullopt;
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T & | operator* () |
| | non-const dereference operator
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const T & | operator* () const |
| | const dereference operator
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bool | operator== (const optional< T > &other) const |
| | equal comparison
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T & | value () & |
| | return the holded value. throws std::logic_error if holding no value
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const T & | value () const & |
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T && | value () && |
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const T && | value () const && |
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| operator bool () const |
| | whether this object is holding a value
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bool | has_value () const |
| | whether this object is holding a value (alternate form).
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template<typename T>
class dmlc::optional< T >
Is not constructible or convertible from any expression of type (possibly const) dmlc::optional<U>, i.e., the following 8 type traits are all false: Link: https://en.cppreference.com/w/cpp/utility/optional/optional.
c++17 compatible optional class.
At any time an optional<T> instance either hold no value (string representation "None") or hold a value of type T.
