Do you create your own code generators?

Question

The Pragmatic Programmer advocates the use of code generators. Do you create code generators on your projects? If yes, what do you use them for?

Answer 1

Code generators if used widely without correct argumentation make code less understandable and decrease maintainability (the same with dynamic SQL by the way). Personally I'm using it with some of ORM tools, because their usage here mostly obvious and sometimes for things like searcher-parser algorithms and grammatic analyzers which are not designed to be maintained "by hands" lately. Cheers.

Answer 2

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 3

In hardware design, it's fairly common practice to do this at several levels of the 'stack'. For instance, I wrote a code generator to emit Verilog for various widths, topologies, and structures of DMA engines and crossbar switches, because the constructs needed to express this parameterization weren't yet mature in the synthesis and simulation tool flows.

It's also routine to emit logical models all the way down to layout data for very regular things that can be expressed and generated algorithmically, like SRAM, cache, and register file structures.

I also spent a fair bit of time writing, essentially, a code generator that would take an XML description of all the registers on a System-on-Chip, and emit HTML (yes, yes, I know about XSLT, I just found emitting it programatically to be more time-effective), Verilog, SystemVerilog, C, Assembly etc. "views" of that data for different teams (front-end and back-end ASIC design, firmware, documentation, etc.) to use (and keep them consistent by virtue of this single XML "codebase"). Does that count?

People also like to write code generators for e.g. taking terse descriptions of very common things, like finite state machines, and mechanically outputting more verbose imperative language code to implement them efficiently (e.g. transition tables and traversal code).

Answer 4

there might be a lot of code generators out there , however I always create my own to make the code more understandable and suit the frameworks and guidelines we are using

Answer 5

Yes I've had to maintain a few. CORBA or some other object communication style of interface is probably the general thing that I think of first. You have object definitions that are provided to you by the interface you are going to talk over but you still have to build those objects up in code. Building and running a code generator is a fairly routine way of doing that. This can become a fairly lengthy compile just to support some legacy communication channel, and since there is a large tendency to put wrappers around CORBA to make it simpler, well things just get worse.

In general if you have a large amount of structures, or just rapidly changing structures that you need to use, but you can't handle the performance hit of building objects through metadata, then your into writing a code generator.

Answer 6

We use a generator for all new code to help ensure that coding standards are followed.

We recently replaced our in-house C++ generator with CodeSmith. We still have to create the templates for the tool, but it seems ideal to not have to maintain the tool ourselves.

Answer 7

My most recent need for a generator was a project that read data from hardware and ultimately posted it to a 'dashboard' UI. In-between were models, properties, presenters, events, interfaces, flags, etc. for several data points. I worked up the framework for a couple data points until I was satisfied that I could live with the design. Then, with the help of some carefully placed comments, I put the "generation" in a visual studio macro, tweaked and cleaned the macro, added the datapoints to a function in the macro to call the generation - and saved several tedious hours (days?) in the end.

Don't underestimate the power of macros :)

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I am also now trying to get my head around CodeRush customization capabilities to help me with some more local generation requirements. There is powerful stuff in there if you need on-the-fly decision making when generating a code block.

Answer 8

in my opinion a good programming language would not need code generators because introspection and runtime code generation would be part of language e.g. in python metaclasses and new module etc.

Answer 9

I have my own code generator that I run against SQL tables. It generates the SQL procedures to access the data, the data access layer and the business logic. It has done wonders in standardising my code and naming conventions. Because it expects certain fields in the database tables (such as an id column and updated datetime column) it has also helped standardise my data design.

Answer 10

I can't think of any projects where we needed to create our own code generators from scratch but there are several where we used preexisting generators. (I have used both Antlr and the Eclipse Modeling Framework for building parsers and models in java for enterprise software.) The beauty of using a code generator that someone else has written is that the authors tend to be experts in that area and have solved problems that I didn't even know existed yet. This saves me time and frustration.

So even though I might be able to write code that solves the problem at hand, I can generate the code a lot faster and there is a good chance that it will be less buggy than anything I write.

Answer 11

code generators usually generate more unmanageable code in long term usage.

however, if it is absolutely imperative to use a code generator (eclipse VE for swing development is what I use at times) then make sure you know what code is being generated. Believe me, you wouldn't want code in your application that you are not familiar with.

Answer 12

It is often useful to create a code generator that generates code from a specification - usually one that has regular tabular rules. It reduces the chance of introducing an error via a typo or omission.

Answer 13

If you're not going to write the code, are you going to be comfortable with someone else's generated code?

Is it cheaper in both time and $$$ in the long run to write your own code or code generator?

I wrote a code generator that would build 100's of classes (java) that would output XML data from database in a DTD or schema compliant manner. The code generation was generally a one time thing and the code would then be smartened up with various business rules etc. The output was for a rather pedantic bank.

Answer 14

In "Pragmatic Programmer" Hunt and Thomas distinguish between Passive and Active code generators.

Passive generators are run-once, after which you edit the result.

Active generators are run as often as desired, and you should never edit the result because it will be replaced.

IMO, the latter are much more valuable because they approach the DRY (don't-repeat-yourself) principle.

If the input information to your program can be split into two parts, the part that changes seldom (A) (like metadata or a DSL), and the part that is different each time the program is run (B)(the live input), you can write a generator program that takes only A as input, and writes out an ad-hoc program that only takes B as input. (Another name for this is partial evaluation.)

The generator program is simpler because it only has to wade through input A, not A and B. Also, it does not have to be fast because it is not run often, and it doesn't have to care about memory leaks.

The ad-hoc program is faster because it's not having to wade through input that is almost always the same (A). It is simpler because it only has to make decisions about input B, not A and B.

It's a good idea for the generated ad-hoc program to be quite readable, so you can more easily find any errors in it. Once you get the errors removed from the generator, they are gone forever.

In one project I worked on, a team designed a complex database application with a design spec two inches thick and a lengthy implementation schedule, fraught with concerns about performance. By writing a code generator, two people did the job in three months, and the source code listings (in C) were about a half-inch thick, and the generated code was so fast as to not be an issue. The ad-hoc program was regenerated weekly, at trivial cost.

So active code generation, when you can use it, is a win-win. And, I think it's no accident that this is exactly what compilers do.

Answer 15

Code generators are work-around for programming language limitations. I personally prefer reflection instead of code generators but I agree that code generators are more flexible and resulting code obviously faster during runtime. I hope, future versions of C# will include some kind of DSL environment.

Answer 16

How many are you looking for? I've created two major ones and numerous minor ones. The first of the major ones allowed me to generate programs 1500 line programs (give or take) that had a strong family resemblance but were attuned to the different tables in a database - and to do that fast, and reliably.

The downside of a code generator is that if there's a bug in the code generated (because the template contains a bug), then there's a lot of fixing to do.

However, for languages or systems where there is a lot of near-repetitious coding to be done, a good (enough) code generator is a boon (and more of a boon than a 'doggle').

Answer 17

The only code generators that I use are webservice parsers. I personally stay away from code generators because of the maintenance problems for new employees or a separate team after hand off.

Answer 18

I write my own code generators, mainly in T-SQL, which are called during the build process.

Based on meta-model data, they generate triggers, logging, C# const declarations, INSERT/UPDATE statements, data model information to check whether the app is running on the expected database schema.

I still need to write a forms generator for increased productivity, more specs and less coding ;)

Answer 19

I've created a few code generators. I had a passive code generator for SQL Stored procedures which used templates. This generated generated 90% of our stored procedures.

Since we made the switch to Entity Framework I've created an active codegenerator using T4 (Text Template Transformation Toolkit) inside visual studio. I've used it to create basic repository partial classes for our entities. Works very nicely and saves a bunch of coding. I also use T4 for decorating the entity classes with certain Attributes.

Answer 20

Yes , I developed my own code generator for AAA protocol Diameter (RFC 3588). It could generate structures and Api's for diameter messages reading from an XML file that described diameter application's grammar.

That greatly reduced the time to develop complete diameter interface (such as SH/CX/RO etc.).

Answer 21

I use code generation features provided by EMF - Eclipse Modeling Framework.

Answer 22

Code generators are really useful in many cases, especially when mapping from one format to another. I've done code generators for IDL to C++, database tables to OO types, and marshalling code just to name a few.

I think the point the authors are trying to make is that if you're a developer you should be able to make the computer work for you. Generating code is just one obvious task to automate.

I once worked with a guy who insisted that he would do our IDL to C++ mapping manually. In the beginning of the project he was able to keep up, because the rest of us were trying to figure out what to do, but eventually he became a bottleneck. I did a code generator in Perl and then we could pretty much do his "work" in a few minutes.