scaladynamiccake-pattern

Scala: Lazy baking and runtime compilation of cake pattern

One of the great limitations of the cake pattern is that its static. I would like to be able to mix-in traits potentially written by different coders completely independently. However the traits would not need to be mixed-in frequently. The user would have an initialisation screen where they would choose the traits / assemblies, before the main application was run. So the thought occurred to me why not mix-in and compile the chosen traits from with in the user choice selection module. If the compilation failed, no problem the user would just get back some message - incompatible assemblies or what ever. If the compilation succeeded then the top UI module would load the newly compiled classes with the pre-compiled parts of the assemblies and run the main application. Note there might only need to be one or two classes compiled duruing run time initialisation. All the rest of the code could have been compiled normally.

I'm pretty new to Scala. Is this a recognised pattern? Is there any support for it? It seems mad to have to use Guice for a relative simple dependency situation. Can I run the Scala compiler easily from within an application? Can I run it in memory and its outputs be used from memory without unnecessary file creation?

Note: Although appearing to be dynamic, this methodology would remain 100% static.

Edit it occurs to that one of the drives of Microsoft's Roslyn project was to enable just this sort of thing for C# and Visual Basic. But that seems to have been a pretty big project even for a high powered Microsoft team.

Solution

  • Calling the compiler directly from within Scala is doable, but not for the timid. Luckily, the good people at Twitter have automated the process for you. (140 character celebrity micro-blogging, and some cool Scala utilities! Thanks Twitter.) You can use the com.twitter.utils.Eval class to compile and evaluate Scala strings. In your example, you would do something like

    val eval = new Eval()
val myObj = eval[BaseClass]("new BaseClass extends " + traitNameList.mkString(" with "))

    This will create you a new object with all of the traits you desire built in. The question then arises as to whether this is a good idea. Downsides: