cppdraft_translate/cppdraft/except/nested.md

[except.nested]

17 Language support library [support]

17.9 Exception handling [support.exception]

17.9.8 nested_exception [except.nested]

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namespace std {class nested_exception {public:constexpr nested_exception() noexcept; constexpr nested_exception(const nested_exception&) noexcept = default; constexpr nested_exception& operator=(const nested_exception&) noexcept = default; constexpr virtual ~nested_exception() = default; // access functionsnoreturn constexpr void rethrow_nested() const; constexpr exception_ptr nested_ptr() const noexcept; }; template noreturn constexpr void throw_with_nested(T&& t); template constexpr void rethrow_if_nested(const E& e);}

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The class nested_exception is designed for use as a mixin through multiple inheritance.

It captures the currently handled exception and stores it for later use.

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[Note 1:

nested_exception has a virtual destructor to make it a polymorphic class.

Its presence can be tested for with dynamic_cast.

— end note]

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constexpr nested_exception() noexcept;

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Effects: The constructor calls current_exception() and stores the returned value.

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[[noreturn]] constexpr void rethrow_nested() const;

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Effects: If nested_ptr() returns a null pointer, the function calls the function std​::​terminate.

Otherwise, it throws the stored exception captured by *this.

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constexpr exception_ptr nested_ptr() const noexcept;

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Returns: The stored exception captured by this nested_exception object.

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template<class T> [[noreturn]] constexpr void throw_with_nested(T&& t);

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Let U be decay_t.

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Preconditions: U meets the Cpp17CopyConstructible requirements.

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Throws: If is_class_v && !is_final_v && !is_base_of_v<nested_exception, U> is true, an exception of unspecified type that is publicly derived from bothU and nested_exception and constructed from std​::​forward(t), otherwisestd​::​forward(t).

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template<class E> constexpr void rethrow_if_nested(const E& e);

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Effects: If E is not a polymorphic class type, or if nested_exception is an inaccessible or ambiguous base class of E, there is no effect.

Otherwise, performs:if (auto p = dynamic_cast<const nested_exception*>(addressof(e))) p->rethrow_nested();