Some days ago I received an email of somebody asking me if I am (still) using T4 templates within the DSL we are building. After reading some of my latest post he got the idea that a lot of the features we are building aren’t implemented in Text templates (T4). He asked me if there is a special reason for that and if I think the T4 templates are useful enough for writing (parts of) your DSL.

Actually it is true that a lot of the things I am currently working on is implemented in pure C# code and is hooked into the diagram itself by using techniques described in earlier posts. For me this works just great.

The thing I like about integrating as many features as possible directly in the diagram itself is that it requires no user actions (selecting menu items) to “execute the feature”. For example, in our DSL you don’t have to select a menu item to translate a Service that is modelled in our Designer into WSDL. This is done on the fly whenever a change is made in the designer and the diagram is still a valid representation of a Service. All of this is done by events that get triggered “automatically” through the designer. Another option was to implement the WSDL generation into T4 templates and let the user trigger the execution of the T4 template through a menu item.

It’s not that I don’t like writing T4 templates! Actually I do like the templates. I have to admit that there are some improvements possible in the “writing experiences” of these templates but I am sure this will improve in future builds of the DSL Tools. I can imagine that we will use the T4 templates for some other artifacts that get generated out of our domain model. To be honest, the WSDL generation for our DSL is besides the “pure C#” version also available in a T4 template. Translating the “pure C#” version into a T4 template (and vice versa) was done in a few minutes.

So, to answer the question in the email that starts me writing this post. A lot of the functionality in our DSL is built in “pure C#” directly hooked into the diagram, but that doesn’t mean that I don’t like T4 templates or think they are not useful! In fact, they will be part of our DSL. I think you have to find out for yourself what features and/or customizations you need in your DSL and what can be best implemented in pure C# and what can be best implemented in T4 templates.

I noticed that George Mathew (team member DSL Tools) wrote one of his first posts on his blog about new features in the Text Templates (T4) of the DSL Tools. Maybe he (or other team members) has some thoughts or better explanation on when to use the T4 templates and when to implement things directly into the designer or diagram?