Rather than join routePrefix to the pattern w/ a slash, how about this?  ```$this->routePrefix . $annotation->getPattern()```
That could possibly allow a prefix to be specified, and then joined to a pattern, without a slash (which is actually something I'd personally like in my own code). So rather than forcing a convention of a slash between prefix & pattern, it would boil down to how the prefix & pattern are defined in the developed app.

I'm thinking I like that approach better, and simplifies the code.