Rule Type.3 is missing an exception. about cppcoreguidelines HOT 8 CLOSED

Remember you can always go from non const to const. The shared implementation could be the const version. Thank you for the suggestion but you can write good code and still be typesafe.

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Andrew, I think you closed this too quickly. Please read this section in Scott Meyer's book -- sorry it was Effective C++, not Effective STL (my mistake) -- (or read the Stack Overflow answers in more detail). You can't just go from a non-const method to a const method:

class A
{
public:
    B& getB()
    {
         // really long code to return access to a B
    }

    const B& getB() const
    {
        // QUESTION: How to do I apply DRY principle by calling 'B& getB()' from here?
        // There is no way.  Trying to do so would be unsafe anyway.
    }

    const C& getC() const
    {
         // really long code to return access to a C.
    }

    C& getC()
    {
        // QUESTION: How to do I apply DRY principle by calling 'const C& getC() const' from here?
        // If I know that the C object the const method returns is actually mutable for a non-const A,
        // then I should be able to call the const method and cast away the constness of the result.
        return const_cast<C&>(static_cast<const A*>(this)->getC());
    }
};

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I also agree with @hallsoftware

I devoted a page for a full example here and the exact reference is

Scott Meyers. Effective C++ (3rd edition). ISBN: 0-321-33487-6. Item 3, paragraph 'Avoid duplication in const and non-const member functions'

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If templates are an option, the following should be a viable way to practice DRY without const_cast in many circumstances. I do this myself with some frequency:

class bar;

class foo
{
public:
    bar& get_bar() { return get_bar_impl(*this); }
    const bar& get_bar() const { return get_bar_impl(*this); }

private:    
    template< class cv_foo >
    static auto get_bar_impl(cv_foo& f) -> decltype(f.get_bar())
    {
        // Now you have access to a properly cv-qualified foo and
        // can get a properly cv-qualified bar reference without
        // possibly silently violating type safety by using const_cast
    }
};

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It looks odd to see this issue open with the 'declined' label. I know the declined label was added when the issue was originally added. Should it be removed now that the issue was reopened?

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Discussed 11/30/2015.

@hallsoftware, thanks for the note. @gdr-at-ms will look more thoroughly.

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Discussed 21 Dec 2015.

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Thanks all, including @john-lynch for the template version (also mentioned on SO).

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