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Naming Conventions for Parameterized Types

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Naming Conventions for Parameterized Types

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Parameterized types - the <> expressions that can be used in Java as of JDK 5 are not just for collections. I find myself frequently using them in APIs I design. They really do let you write things which are more generic in the non-Java sense of the word - and the result is more reusable code, which means less code overall, which means fewer bugs and things to test. The verbosity, and some of the weirdness of type-erasure are less than ideal, but used right, the benefits are worth the complexity.

The standard (and somewhere recommended) naming convention for parameterized types is to use a single-letter name. That works fine in signatures that have only one such type. But in practice, single-letter names make code less self-describing, and if you're defining a class with more than one parameterized type, it can be confusing and hard to read. People other than me will have to call, understand and maintain my code - the more self-describing I can make it, the better.

So I am looking for a naming convention that makes it obvious that something is a parameterized type, but allows for descriptive names. I am wondering if anybody else has run into this problem, and if there is any emerging consensus on naming generics. Do you work on a project that uses generics a lot? If so, what do you do?

Here's an example. At the moment, I'm writing a generic (in both senses) class which simply limits the number of threads which can access some resource. It's basically a wrapper around a Semaphore which uses a Runnable-like object to ensure that the Semaphore is accessed correctly, and does some non-blocking statistic gathering about thread contention. So to access the scarce resource, you pass in a ResourceAccessor:

    public interface ResourceAccessor <ProtectedResource, Argument, Result> {
        public Result run (ProtectedResource resource, Argument argument);
    }
The problem is that, when somebody looks at this interface, they will instantly get the idea that there are really classes they need to go find, which are called ProtectedResource, Argument and Result - and of course, no such classes exist - these are just names for generic types.
The standard-naming-convention is worse:
    public interface ResourceAccessor <T, R, S> {
        public S run (T resource, R argument);
    }

Here, nobody could possibly figure out what on earth this class is for without extensive documentation - this is a really horrible idea. So I've concluded that the standard recommendations for generic type names are simply wrong for any non-trivial usage (I.e. Collection<T> is fine, since there is one type and Collections are well-understood). You simply can't do this on a non-collection code structure you have invented, or people will just be confused and not use it.


The best suggestion I've heard thus far is using $ as a prefix:

    public interface ResourceAccessor <$ProtectedResource, $Argument, $Result> {
        public $Result run ($ProtectedResource resource, $Argument argument);
    }

I don't find this pretty, but I don't have any better ideas, and at least it makes it crystal-clear that there is something different about these names.

Any thoughts? What do you do in this situation?

How do you break a Monolith into Microservices at Scale? This ebook shows strategies and techniques for building scalable and resilient microservices.

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