[boost] An attempt to generalize the Pimpl idom with properly separated interface and implementation

From: Vladimir Batov (batov_at_[hidden])
Date: 2007-10-05 12:39:10

Given I've been using this Pimpl idiom quite extensively lately I've noticed 
writing the same scaffolding over and over again. Being the lazy bugger as I 
am I looked around if there was anything available. Turns out there were 
proposals floated around (like Asger Mangaard's dated around May 2006). 
However, I did not see anything that would preserve idiom's original 
purpose/value - the separation of interface and implementation. So, I jogged 
something with that in mind. That seemed to do the job for me as something 
tedious like

class Test
{
    public:

    Test (int);
    Test (int, int);

    int get() const;

    bool operator==(Test const& p) const { return impl_ == p.impl_; }
    bool operator!=(Test const& p) const { return impl_ != p.impl_; }
    operator bool() const { return implementation_; }

    void swap(pimpl& that) { impl_.swap(that.impl_); }

    private:

    struct Internal;
    boost::shared_ptr<Internal> impl_;
};

shrunk down do pure interface

struct Test : public boost::pimpl<Test>
{
    Test (int);
    Test (int, int);

    int get() const;
};

with implementation details safely tacked away in an implementation file. 
However, it looked suspiciously easy. So, I am throwing it out for all the 
respected community to see (uploaded as vb_pimpl_0.1.zip) and to set me 
straight. Is there any value in that basic idea? Don't hold back your 
criticism.

Regards,
Vladimir.