[except.nested] (original) (raw)

17 Language support library [support]

17.9 Exception handling [support.exception]

17.9.7 nested_­exception [except.nested]

namespace std { class nested_exception { public: nested_exception() noexcept; nested_exception(const nested_exception&) noexcept = default; nested_exception& operator=(const nested_exception&) noexcept = default; virtual ~nested_exception() = default;

// access functions
[[noreturn]] void rethrow_nested() const;
exception_ptr nested_ptr() const noexcept;

};

template [[noreturn]] void throw_with_nested(T&& t); template void rethrow_if_nested(const E& e); }

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.

[ Note

:

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

Its presence can be tested for with dynamic_­cast.

— end note

]

nested_exception() noexcept;

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

[[noreturn]] void rethrow_nested() const;

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

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

exception_ptr nested_ptr() const noexcept;

Returns:The stored exception captured by this nested_­exception object.

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

Preconditions: U meets the Cpp17CopyConstructible requirements.

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

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

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();