Are code generators bad?

Question

I use MyGeneration along with nHibernate to create the basic POCO objects and XML mapping files. I have heard some people say they think code generators are not a good idea. Wha

Answer 1

Code generators can be a boon for productivity, but there are a few things to look for:

Let you work the way you want to work.

If you have to bend your non-generated code to fit around the generated code, then you should probably choose a different approach.

Run as part of your regular build.

The output should be generated to an intermediates directory, and not be checked in to source control. The input must be checked in to source control, however.

No install

Ideally, you check the tool in to source control, too. Making people install things when preparing a new build machine is bad news. For example, if you branch, you want to be able to version the tools with the code.

If you must, make a single script that will take a clean machine with a copy of the source tree, and configure the machine as required. Fully automated, please.

No editing output

You shouldn't have to edit the output. If the output isn't useful enough as-is, then the tool isn't working for you.

Also, the output should clearly state that it is a generated file & should not be edited.

Readable output

The output should be written & formatted well. You want to be able to open the output & read it without a lot of trouble.

#line

Many languages support something like a #line directive, which lets you map the contents of the output back to the input, for example when producing compiler error messages or when stepping in the debugger. This can be useful, but it can also be annoying unless done really well, so it's not a requirement.

Answer 2

My stance is that code generators are not bad, but MANY uses of them are.

If you are using a code generator for time savings that writes good code, then great, but often times it is not optimized, or adds a lot of overhead, in those cases I think it is bad.

Answer 3

We use code generators for generating data entity classes, database objects (like triggers, stored procs), service proxies etc. Anywhere you see lot of repititive code following a pattern and lot of manual work involved, code generators can help. But, you should not use it too much to the extend that maintainability is a pain. Some issues also arise if you want to regenerate them.

Tools like Visual Studio, Codesmith have their own templates for most of the common tasks and make this process easier. But, it is easy to roll out on your own.

Answer 4

I use My Generation with Entity Spaces and I don't have any issues with it. If I have a schema change I just regenerate the classes and it all works out just fine.

Answer 5

The best application of a code generator is when the entire project is a model, and all the project's source code is generated from that model. I am not talking UML and related crap. In this case, the project model also contains custom code.

Then the only thing developers have to care about is the model. A simple architectural change may result in instant modification of thousands of source code lines. But everything remains in sync.

This is IMHO the best approach. Sound utopic? At least I know it's not ;) The near future will tell.

Answer 6

Code generated by a code-generator should not (as a generalisation) be used in a situation where it is subsequently edited by human intervention. Some systems such the wizards on various incarnations of Visual C++ generated code that the programmer was then expected to edit by hand. This was not popular as it required developers to pick apart the generated code, understand it and make modifications. It also meant that the generation process was one shot.

Generated code should live in separate files from other code in the system and only be generated from the generator. The generated code code should be clearly marked as such to indicate that people shouldn't modify it. I have had occasion to do quite a few code-generation systems of one sort or another and All of the code so generated has something like this in the preamble:

-- =============================================================
-- === Foobar Module ===========================================
-- =============================================================
--
--         === THIS IS GENERATED CODE.  DO NOT EDIT. ===
--
-- =============================================================

Code Generation in Action is quite a good book on the subject.