Updating Classes and function

Question

Assume we have a class called "MyClass"

Public Class MyClass

End Class

this class has a function called "My function"

Public Class MyClass
    Public Function MyFunction()

    End Function
End Class

This class has been implemented for some time and its been working fine. Now we need to change the implementation of the function "MyFunction". One option would be to open the source code and change it there. But I'm guessing there has to be a better approach.

Inheritance comes to mind but I don't want to change the derived classes name. I want the name of the class to still remain "MyClass", But I'm guessing the code below will cause an error:

Public Class MyClass
    Inherits MyClass
    Public Function MyFunction()

    End Function
End Class

In other words I'm trying to create a new version of the old class by keeping most of the members the same but just changing a few functions.

To explain the project as a whole, The program is meant for structural design. What it does it designs structural components (i.e columns, beams, slabs, ...). The design procedures are specified by 3rd parties (government regulations). For example: In the year 2007 government regulations specified that column dimensions are to satisfy the equation F:

H*B < Fy^2/L

In the year 2008 they introduced a new function G and they say column dimensions must satisfy this new function:

H*B^2 < Fy^0.5/E+Alpha^2/L

Where H and B are column dimensions.

What I don't want to do is to open the source code every year and make these changes. I want to somehow override the functions that need to be changed without opening the source.

Any Ideas?

Many reasons. Don't want other programmers to have access to the source, the code is huge don't want people messing around in there, .. — Math4123, Aug 18 '14 at 06:36
Messing around with the software's architecture is the wrong place to protect source code. A version control system with access control would be more appropriate. Furthermore, you can add comments to the source file which indicate that the function is not to be modified and hope people will respect that. — Nico Schertler, Aug 18 '14 at 07:30
Using the same name for more than one class is impossible because the compiler cannot unambiguously resolve those classes' usages. As Nico Schertler stated before, use version control if you want to keep your initial implementation. If your new implementation of `MyFunction` yields a different result, you should definitly choose a new descriptive name. If it does not, I see no reason to keep the old code at all. — DMAN, Aug 18 '14 at 09:15
Thanks for the info guys. But my question is actually how do I create a new version of the class. (with the same name) — Math4123, Aug 18 '14 at 12:11
If you want to use the same name, you'll have to use a different namespace. Maybe call it MyNamespace2. It's hard to know what your problem really is, this makes it difficult to give you good tips. — the_lotus, Aug 18 '14 at 13:18
@the_lotus Thanks, I've provided more explanation about the project. — Math4123, Aug 18 '14 at 14:01
These values shouldn't be hardcoded in the function, they should be in a database and the program should be able to figure out wich setting to get for a specific year (you might want to get historical information). Your function could pass a year: MyFunction(ByVal year As Integer) — the_lotus, Aug 18 '14 at 15:12
@the_lotus Thanks again, I've updated the project description a bit. The 65X35 was a wrong example. Its not the numbers that change but rather the functions as a whole. — Math4123, Aug 19 '14 at 06:00
I have edited your title. Please see, "[Should questions include “tags” in their titles?](http://meta.stackexchange.com/questions/19190/)", where the consensus is "no, they should not". — John Saunders, Aug 19 '14 at 06:01

Victor Zakharov · Answer 1 · 2014-08-19T11:23:29.480

The code is generally not supposed to be changed over time. That is - if you wrote code that is guaranteed to break after 2 weeks by itself, you probably should reconsider your design.

As you rules/regulations come out, you usually update your input data (in a form of XML, or a relational database for large amounts of data), and your program would automatically pick those up.

The only case you would update your program under this scenario is when new type of regulations come out. But even in this case the changes are usually minimal.

A good anti-pattern example for this - you have 500 forms, each of them has 500 lines of code, so that's 250000 lines of code in your UI layer. New regulations come out that requires changing 50% of the code in each form. Your impact is 125000, which at 40 lines of code per day would take 8.5 developer-years.

A solution to this would be having a change of 100 lines spread across all forms, adding 1 line in each, or leaving everything as is. Also there will be a data load/conversion procedure from a government/other file, which populates your database in the proper format, updating the values or adding new ones. There may be 10 lines of change in that program, but that's about it, 3 days worth of work, if you believe in 40 LoC per day. Otherwise it still falls under 2 weeks of developer's time.

Depending on how you implement it, the benefit of this approach could be that you support old standards as well, so older input can be matched and production reports can be generated. It is a good practice to be able to back-date your reports, cause sometimes there are issues in report code left unnoticed for months before being discovered.

EDIT: A more structured approach to what I suggested in the comments would be storing expression trees in the DB. Most simple form of it is just a linear workflow, using postfix notation (single table). For example A, B, + C - is equivalent to A + B - C. You can then have a user interface for some configuration tool, which only allows user to input values and functions that are applicable. This is assuming applicable values are also stored in DB as parameters (one structural component can have 0...N of them).

Thanks for the info. I've changed the description a bit. Its not the input data that changes but rather the functions as a whole. — Math4123, Aug 19 '14 at 06:04
@VBAProgrammer: Did you consider storing your expression as a String, and the evaluating as a string? You can substitute parameters and then evaluate as a constant expression, or use directly with parameters, depending on what framework supports. Check this out: [Is there a string math evaluator in .NET?](http://stackoverflow.com/questions/355062/is-there-a-string-math-evaluator-in-net) — Victor Zakharov, Aug 19 '14 at 11:02

Gridly · Answer 2 · 2014-08-18T15:52:41.917

Inheritance can do what you want but you need to create a new ancestor, not descendant.

Change the name of the original class to something that denotes that it is a base class. Also, add the MustInherit modifier to the class and Overridable to any of the methods or properties that you may need to override.

One thing to watch for is Private members in this base class. Any members that need to be accessible from the descendant class cannot be Private and must be changed to Protected.

The original class looks like this.

Public MustInherit Class MyBaseClass
    Public Overridable Function MyFunction() As String
        ' code...
    End Function

    Public Overridable Function AnotherFunction() As String
        ' code...
    End Function

End Class

Now create a new class with the original class's name which inherits from the base class. Override just the members that need to be different.

Public Class MyClass
    Inherits MyBaseClass

    Public Overrides Function MyFunction() As String
        ' new code...
    End Function

End Class

That will get you started. The Template Pattern will allow you to do more fine grained code changes where only parts of a method need to be changed.

Thanks for the info, but this will not help. Every year I will have to open the source code of the previous year and change the base class names. Thats not what I'm trying to do. — Math4123, Aug 19 '14 at 06:02

score 0 · Answer 3 · edited May 23 '17 at 10:33

The formula is a bit complicated and you'll still need to change some code unless you store these in a database somehow.

An option would be to use inheritance with a factory method.

Public Class BaseClass

    Public MustOverride Function MyFunction()

    Public Function GetInstance(ByVal year As Integer) As BaseClass

        If year = 2007 Then Return New Class2007()
        If Year = 2008 Then Return New Class2008()

    End Function

End Class

Public Class Class2007
    Inherits BaseClass

    Public Overrides Function MyFunction()
        ' H*B < Fy^2/L
    End Function

End Class

Public Class Class2008
    Inherits BaseClass

    Public Overrides Function MyFunction()
        ' H*B^2 < Fy^0.5/E+Alpha^2/L
    End Function

End Class

then, everywhere in your code you use BaseClass never knowing that Class2007 and Class2008 exists

Dim o As BaseClass

o = BaseClass.GetInstance(2007)
o.MyFunction()

Depending on the need, this can also be done with interface.

If you need to store the formulas in the database as string, you'll need to get a parser and this can also be found using 3rd party library. https://stackoverflow.com/questions/1387430/recommended-math-library-for-c-net

Updating Classes and function

3 Answers3