Re: [boost] A Pimpl variant

Subject: Re: [boost] A Pimpl variant
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2010-04-02 13:00:21

vicente.botet wrote:
>
> My experience is that I add more private member functions
> than private member data. I have explored a different variant
> 5.         Put all private funtion and static data (but not
> instance data) into XImpl. XImpl needs only to store the back pointer.

[snip]

> class C {
> public:
>     void f();
>     void g();
> protected:
>  // ...
> private:
>   struct impl;
>   friend struct impl;
>   // the private part contains only instance data and virtual
> functions
>   int priv;
> };
>
> * Identify the private functions and the private static data
> and put them on the implementation class
>
> struct C::impl {
>   C::impl(C* thisC) : that(*thisC) {}
>   void ifct() {
>     that.priv = ... // use of private data
>     that.g();         // call to a public function
>     jfct();             // call another private function
>   }
>   C& that;
>   static int icount;
> };
>
> * Prefix all the ex private function calls by impl(this)  impl(this).ifct();
> * Access without constraints the impl static data  impl::icount;

Wouldn't it be simpler to use static member functions?

struct C::impl
{
   static void
   ifct(C * _this)
   {
      _this->priv = ... // use private data
      _this->g(); // call public member function
      ...
   }
};

Using it from C member functions would be straightforward:

   void
   C::f()
   {
      impl::ifct(this);
      // compare: impl(this).ifct();
      ++impl::icount;
   }

The definition of impl is simpler in my version and invoking impl member functions is one (!) character shorter.  Your version requires an implicit this argument from which "that" is found; mine makes your "that" the sole argument, so its potentially faster.  For those that like "this->" in front of member access, mine even looks similar (in impl's member functions).

_____
Rob Stewart                           robert.stewart_at_[hidden]
Software Engineer, Core Software      using std::disclaimer;
Susquehanna International Group, LLP  http://www.sig.com

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