Are the implicit move ctor/assignmet operations noexcept? What about implicit copy operations?

Question

The question titles says it all. I need to know if the default copy/move assignment/ctors implemented implicitly by the compiler are declared noexcept.

Answer 1

The standard says:

An inheriting constructor (12.9) and an implicitly declared special member function (Clause 12) have an exception-specification. If f is an inheriting constructor or an implicitly declared default constructor, copy constructor, move constructor, destructor, copy assignment operator, or move assignment operator, its implicit exception-specification specifies the type-id T if and only if T is allowed by the exception-specification of a function directly invoked by f’s implicit definition; f allows all exceptions if any function it directly invokes allows all exceptions, and f has the exception-specification noexcept(true) if every function it directly invokes allows no exceptions.

So if the implicitly declared copy/move assignment/ctors of your class do not need to call anything that is marked noexcept(false) then they will have the noexcept(true) specifier. The functions that need to be called will be the copy/move assignment/ctors of base class and non-static data members.

Answer 2

Obviously they can't just be unconditionally noexcept, that would be both silly and wrong (for example, the implicit copy constructor for a class containing a std::string member might need to allocate memory, so it can't sensibly be noexcept).

They're noexcept if they only call functions that are noexcept, and they're not noexcept if they call any functions that are not noexcept.