Daniel Lidström <somebody@microsoft.com> wrote:

> // In the header of your class called Line
>
> #include <string>
>
> class Line
> {
> public:
>
> Line(const std::string& name);
> const std::string& GetName() const;
> void SetName(const std::string& s);
>
> private:
>
> // Private implementation idiom:
> // all member variables are hidden in this class
> class LineImpl;
> const LineImpl& m_pimpl; // normally a non-const pointer
> };
>
> // and in your implementation file:
>
> #include "Line.h"
>
> // Here we define the class with the member variables
> class Line::LineImpl
> {
> public:
>
> LineImpl(const std::string& s) : m_s(s) {}
> // all methods need to be const here
> const std::string& GetName() const { return m_s; }
> void SetName(const std::string& s) const { m_s = s; }
>
> private:
>
> mutable std::string m_s; // the trick! all members are mutable
> };
>
> // create the pimpl instance without using new
> Line::Line(const std::string& s) : m_pimpl(LineImpl(s)) {}

Where would the memory for the LineImpl object be placed? It isn't
embedded in the object, nor is it in the heap, and it can't be placed on
the stack (and still survive the call to the c_tor.)

Doesn't sound like a good idea to me.