Re: extending c++ classes and enumerations

From:

"James Kanze" <james.kanze@gmail.com>

Newsgroups:

comp.lang.c++.moderated

Date:

7 Dec 2006 12:12:33 -0500

Message-ID:

<1165486181.291246.80150@f1g2000cwa.googlegroups.com>

perrog@gmail.com wrote:

James Kanze skrev:

perrog@gmail.com wrote:

I have some question about a C++ syntax that can extend classes and
enumerations.

You've got this already, just with a slightly different syntax.
Use the keyword struct, instead of class, and use free functions
taking a pointer to the type as first parameter, rather than
member functions. You can extend to your hearts desire.

The drawbacks is that you miss all lexical benefits C++will give you.

Such as? The real benefit of class over struct isn't lexical.
The real benefit is improved encapsulation.

:-) Both old Pascal and modern JavaScript supports encapsulation with
the WITH-statement.

Hmmm. Most of the coding guidelines I'm aware of for Pascal ban
the use of WITH, because it rapidly results in unreadable code.
Other than that, I don't see any relationship of WITH with
encapsulation.

Secondly, XML parser Expat can be a sample how difficult it is to read
such source. The first time I saw Expat source-code I thought it was
written in C++ and then preprocessed into C with some utility parser.

Thirdly, projects that uses "light C++" (not using RTTI, templates and
exceptions in the code) only use C++ for these "lexical benefits", and
I can give examples of such project.

Again, I don't know what "lexical benefits" you're talking
about. The important difference between class in C++ and struct
in C is access control, and allowing extension of a class blows
that away.

Adding support for extending classes is hopefully a toll-free change if
it is limited to static and non-virtual functions.

Adding support for extending classes breaks encapsulation.
Completely and thoroughly. It returns C++ back to the level of
C.

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