Re: A Change In Terminology: Monomorphic Objects. Polymorphic Objects

From:

"Le Chaud Lapin" <jaibuduvin@gmail.com>

Newsgroups:

comp.lang.c++.moderated

Date:

3 Jan 2007 15:39:23 -0500

Message-ID:

<1167852400.568644.183880@42g2000cwt.googlegroups.com>

Dave Harris wrote:

In headers, instead of code like:

     #include "MySpecialControl.h"

     struct MyDialog : Dialog {
         MySpecialControl m_control;
         // ...
     };

I am likely to have:

     struct MySpecialControl;

     struct MyDialog : Dialog {
         MySpecialControl *m_pControl;
         // ...
     };

So that client code can #include "MyDialog.h" without getting a dependency
on MySpecialControl.h. This kind of dependency management is important for
large projects.

Yes, the PIMP idiom. I have never liked it, especially if it is used
for the reason you mention. In fact, I seek every opportunity to
create precisely that dependency that you want to avoid. I want the
compiler to see the type that is MySpecialControl. I want the
compiler-generated constructor of MyDialog to auto-construct m_control.
I want the compiler-generated destructor to auto-desstruct m_control.
I want the compiler-generated assignment between two MyDialog's to
automatically assigned (correctly) m_control.

Some might say that not using PIMP will result in too many compilations
of too many files. I say, if you have a class such that, perturbing it
causes the compilation of 1000's of files, then there are one of two
possibilities:

1. The included class is fundamental, and therefore the compilations
are warranted.
2. The organization of the code is poor, and should be restructured to
remove superfluous dependencies.

I think that the extra wait for the compilation to finish after the
perturbation of a critical class is by far the lesser of two evils.

-Le Chaud Lapin-

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