Facebook releases software that creates more software

"Developers outside of Facebook can use this tool to raise the level of abstraction in their code and build more powerful frameworks," wrote Alejandro Marcu, a software engineer at Facebook, about CodeGen, in an e-mail.

Frameworks have been immensely valuable in software development because they save a lot of time in developing a new application by streamlining many of the low-level implementation chores. For instance, the Ruby-On-Rails framework proved to be immensely popular for quickly setting up Web applications.

Frameworks are declarative, meaning that they allow the developer to "write what they want instead of how they want it done," Marcu explained.

Codegen works with Hack, a PHP-like programming language Facebook created to expedite the development of its Web site, and subsequently released as open source for others to use.

Prior to using Codegen, Facebook engineers used a patchwork of scripts and templates to generate the bits of code that perform simple but frequently executed tasks, such as fetching a user's birthday.

This cobblework approach had some limitations though, as Marcu outlined in a blog post explaining the technology. Facebook engineers couldn't tell which parts of the resulting code relied on other parts. So, making any changes could lead to unintended consequences.

Also, this old approach wouldn't allow developers to set data types for variables, which can be handy for ensuring data integrity. Setting data types would also provide a way for code editing software to autocomplete code snippets, another time saver.

And even with the templates, they still had to write many additional components by hand, such as test code, or data loader.

The Codegen library simplifies operations by allowing a developer to create a schema, which would hold a template of code that can be used multiple times, as well as a way to generate all the related functionality needed to support that code, such as a data loader and a connection to the database.

Using the library, the user provides the needed details about the particular implementation and the software does the rest. It can generate classes, methods, variables, functions, interfaces, files, and other commonly needed blocks of code.

 The software also provides a way to identify when  automatically generated code is changed later by another developer, information that can be used to alert an update process not to overwrite the hand-written code. It also provides a place within the generated code to put additional functionality where it won't get overwritten.

Outside of Facebook, the Codegen library would be useful for any developer who routinely needs to make changes across multiple parts of a code base, such as creating a creating a class, or adding a constant.

"Codegen will allow you to automatically do that with one change," Marcu wrote.