std::auto_ptr or boost::shared_ptr for pImpl idiom?

Question

When using the pImpl idiom is it preferable to use a boost:shared_ptr instead of a std::auto_ptr? I\'m sure I once read that the boost version is

Answer 1

If you want a copyable class, use scoped_ptr, which forbids copying, thus making your class hard to use wrong by default (compared to using shared_ptr, the compiler won't emit copy facilities on its own; and in case of shared_ptr, if you don't know what you do [which is often enough the case even for wizards], there would be strange behaviour when suddenly a copy of something also modifies that something), and then out-define a copy-constructor and copy-assignment:

class CopyableFoo {
public:
    ...
    CopyableFoo (const CopyableFoo&);
    CopyableFoo& operator= (const CopyableFoo&);
private:
    scoped_ptr impl_;
};

...
CopyableFoo (const CopyableFoo& rhs)
    : impl_(new Impl (*rhs.impl_))
{}