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Date: Mon, 17 Jun 2002 14:07:21 -0400
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Subject: Re: more to ada paper critic
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Date: 2002-06-17T14:07:21-04:00
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Ted Dennison wrote:
> This must be a C++ idiom with which I'm unfamiliar. I thought C++
> class declarations did not allow any part of the class's declaration
> (like one of its fields) to be declared in a separate compilation.

You're right. I think he's talking about the so-called "pimpl" technique,
which isolates the implementation of a class into a file which is never
seen by the user. The user only sees a class which has a set of methods,
and one pointer to an implementation class.

//-----widget.h-------
class WidgetImpl; // forward declare class
class Widget
{
	auto_ptr<WidgetImpl> pImpl; // OK for WidgetImpl to be incomplete type
public:
	Widget();
	void method1();
	void method2();
};
//-----widget.cpp-----
class WidgetImpl
{
public:
	void method1() { }
	void method2() { }
};
Widget::Widget() : pImpl(new WidgetImpl) { }
void Widget::method1() { pImpl->method1(); }
void Widget::method2() { pImpl->method2(); }