Linking of Classes
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    Because methods are not usually called directly, but invoked via a
    message, it is not possible for the linker to automatically link in the
    methods that are required by a particular application.  This is why all
    the methods for a class are usually defined in the same module as the
    class declaration, so that all the methods of a class are linked in
    along with the class function, whether they are used in the linked
    application or not.

    This is an inevitable consequence of dynamic binding in an object
    oriented system.  Even (mostly) statically bound C++ is not immune to
    this effect.

    Those who have experienced memory problems with Clipper in the past may
    shudder at the idea of linking in procedures which are not necessary at
    runtime, but it is not as bad as it sounds.  The code overlaying system
    in Clipper 5.x was designed with such systems in mind.  In fact, the
    ceiling for program size under Clipper 5.x is likely to be related to
    the size of the symbol table rather than actual code size.  The fact
    that all major linkers for Clipper perform symbol table compaction will
    help here, however.

    Object-oriented systems, especially in the Clipper world, also tend to
    be more data driven than their procedural counterparts, resulting in
    smaller code sizes.

    The point is that in general one should not try to optimize classes by
    using external methods, since this results in what amounts to manual
    linking.

    However, a good design practice which should be followed in any case,
    is to keep individual classes small.  Large, single, 'do-everything'
    classes should be avoided.  Functionality should be added by
    inheritance.  When choosing which class to use for a particular
    purpose, in most cases it should be possible to choose a class at the
    correct level of the inheritance tree such that a minimum of
    uneccessary methods are linked in.