I think `predicate.to_s` would be more idiomatic here since there is nothing else in the String but `predicate`. It is also faster:

```
$ time ruby -e '1000000.times { "#{:sym}"}'

real	0m0.314s
user	0m0.307s
sys	0m0.006s
$ time ruby -e '1000000.times { :sym.to_s }'

real	0m0.204s
user	0m0.196s
sys	0m0.006s
```