NOTES ON THE LISTINGS FILES FOR "TYPING YOUR DATA":

The download files for this article include two complete sets of
files.  The first are those discussed in the text: TYPES.H,
TYPES.CPP, and TYPEDEMO.CPP.  These files implement a simple
database from three data types.  A second set of files is
provided that were too long to include in the text.  These allow
for strings plus the five major numeric types from int to long
double.  The code for typed values gets long fast as you add
types -- it tends to increase by the square of the types.  That's
because each class has to support operations with each of the
other classes.  The code doesn't really get more complex, just a
lot longer.

When you do something like this, it's best to start with two or
maybe three data types to get all the basics sorted out.  Then
you can take advantage of the strong symmetry in the code to add
the additional types using your debugged code as a model.  This
is especially important since the floating point types add other
problems that aren't really germane to the basic algorithm.  For
example, a double can be too small as well too large to convert
into a float.  That is, it can be a value too close to zero.

That's moderately interesting, and you can see how to deal with
it in TYPESALL.CPP, but it doesn't really have anything to do
with the basic objective of creating typed data objects.  It's
best to defer such questions until you have your basic set of
methods worked out.  The files with all of the numeric types
represented are TYPESALL.H and TYPESALL.CPP.  This version of the
value objects works with the original demo program just as well,
since that's the point of encapsulation.  But TYPEDEMO.CPP
doesn't include functions to assert the extra types, so I wrote a
second demo program, TYPEDEM2.CPP, to show off the expanded
definition of types.

To compile the examples, put TYPES.H and TYPESALL.H in your
include directory.  Create one project with TYPES.CPP and
TYPEDEMO.CPP, and another project with TYPESALL.CPP and
TYPEDEM2.CPP.  To use typed data objects in your own projects,
just add TYPESALL.CPP to your own project and include
<TYPESALL.H> in your source code.  For simplicity, delete the
reduced version files used in the article, and then rename the
full version files as TYPES.H and TYPES.CPP.

                              --Gary W. Sims