good or bad practice to make pure virtual functions noexcept [duplicate]

Question

Is it good or bad practice to make pure virtual functions noexcept? I always thought we should not put extra restriction on its implementation classes that their implementation should be no throw since putting this may result in modification in implementation and unnecessary try catch blocks to prevent exception escape. i thought implementation should decide whether function can marked as noexcept not the exception specification should decide implementation?

Can some one please correct me if i am wrong here?

Answer 1

noexcept is part of member function specification, in the same way as its return type, parameter list, and const qualifier. It is there to help users of the function - obviously, at the expense of function's implementers.

If you need to give implementers more flexibility while providing your users with a noexcept function, make a pair of functions - a non-virtual public function with noexcept, and a protected virtual function without noexcept. Make the public noexcept function call virtual implementation, and handle exceptions to hide them from its callers:

class Base {
protected:
    virtual void doSomethingImpl() = 0;
public:
    void doSomething() noexcept {
        try {
            doSomethingImpl();
        } catch(...) {
            // Provide some handling here
        }
    }
};

class Derived : public Base {
    void doSomethingImpl() {
        ... // Implementers have flexibility to throw here
    }
}