This is going to be the first in a series of items about Code Generation, automatically generating your code. I have posted a couple of times previously on this topic, here and here, but I thought a series of posts would be useful, so here is the first.
The Last One
I remember back in the 80s a UK company built a program called ‘The Last One’, its premise being that it was the last computer program because it would write every program from thereon after. Now, after you have picked yourself up off of the floor and stopped laughing, think about it somewhat objectively. Remember, this was in the days of largely batch programs, they started at the beginning, went through a file of instructions or updates, and reacted to each item encountered. As such, with some very clear rules, it shouldn’t be too hard to write a program to read those rules and then process the data files according to those rules. Of course, it would all soon get messy, the types of rules are infinite, and the types of data is also infinite, so some severe constraints would have to be imposed, but wouldn’t a program that can handle multiple applications, even if those applications have to adapt somewhat to that program, be beneficial (of course, you could say this is exactly the same as the SAP paradigm, but please, let’s not talk about SAP when I am feeling good). Event driven applications add a whole new, more difficult dimension of course, but still…
I am a great fan of code generation, using it frequently, and always look for further opportunities to use it. Why do I think it is so good? There are many reasons:
- maintenance is reduced, make a small change and rerun and all code affected by that change will be re-generated
- the quality is improved, all changes are re-generated, no need to remember what needs changing
- the work is done in the more critical and interesting areas, in analysis and design.
To me that third point is the most important. Code generation makes you think about the application requirements and how they should be implemented, something you should do by right, but something that cannot be avoided or done half-heartedly when using code generation. As the design is so critical, and as I find it more interesting than cutting code, this suits me perfectly.
The greatest exponent of code generation that I am aware of is Kathleen Dollard. Her book, Code Generation in Microsft .NET, is the definitive work on the subject, a remarkably comprehensive work that provide end-to-end solutions using XSLT-based code generation based upon a series of templates. As she says … Code generation will turbo-charge your development cycles by offering speed, reusability, agility, and consistency.
Whilst this is a remarkable piece of work, I think that many might find it daunting, even off-putting. The solution is comprehensive, but it is based upon .NET and XML, and dare I say, can even been too purist for the tyros amongst us. For this reason, I will address code generation from a much simpler starting point, show how you can use code generation today using Excel, and build upon it over the next few weeks,
Excel & Code Generation
What I have described so far are full-blown applications, with their attendant complexity, which might discourage you from going any further. But let’s step back a bit, and think about ways in which we can generate code in small doses. Later items will go further, but we can show immediate benefits. In these examples, we will use Excel as the code generating engine. Excel is a superb tool for this, as it is with so many other things, with the grid for our data input, and VBA to handle any complex code generating algorithms.
You may not be aware of it, but maybe you are already using Excel to do code generation. If you ever have a list in Excel, and use formulas and functions to create some more descriptive text that you cut and paste into a code module, that is a simple form of code generation.
Let’s take a simple example. I use class modules a lot, and I find that creating properties is a pain, you need to define a private variable where the actual value is stored, and then Get and Let properties so that the property can be read from and written to in the class (that is assuming two things, your property is read/write, they may not all be so; that you don’t use Public variables for read/write properties – I don’t, I always declare Get and Let).
Using code generation, all we need are two pieces of information, the property name and its data type. If we want to cater for some properties being read only, we need a third denoting the access mode.
So, we can create a spreadsheet with 3 columns
- column A – property name – free format text
column B – data type – Long, Double, String,
Boolean, Range (should suffice for now) – an ideal candidate for a data
- column C – access mode – R, W, or RW – again another dv list
It would be wise to add a fourth, column D, derived column, that takes the property name and replaces any spaces with _, and removes any special characters, as this will be used in the class.
With a few simple formulae, we can easily generate all 3 elements of the property that the class needs,
=”Private m_”&D2&” As “&D2
“Public Property Get “&$D2&”() As ” &$B2&CHAR(10)&
“ “&$D2&” = m_”&$D2&CHAR(10)&”End Property”,
“Public Property Let “&$D2&”() As ” &$B2&CHAR(10)&
” m_ “&$D2&” = “&$D2&CHAR(10)&”End Property”,
“Public Property Let “&$D2&”(ByVal val As ” &$B2&”)”&CHAR(10)&
” m_”&$D2&” = val”&CHAR(10)&”End Property”,
That is all there is to it. Create a list of properties with their attributes, and Excel generates the class code for you, all you need to do is cut and paste it into the class module.
Next time, we will show how to use VBA to write back this data into the class code, after all, one of the primary aims of code generation is to save us from the boring bits. We will also look at a slightly more complex generation.
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