'defined?' is buggy in ruby 2.5.0, which under certain circumstances
users using rack-attack can hit. See issue #253.
I reported (https://bugs.ruby-lang.org/issues/14407) and
fixed (https://github.com/ruby/ruby/pull/1800) the issue in
ruby already, but i guess i would take some time before there's
a new ruby release including that fix.
So for now we would need to circumvent this bug by using
'const_defined?' instead of 'defined?' for this particular case.
More details:
Anyone using:
* ruby 2.5.0
* redis
* rack-attack without redis-store and using at least one throttle
* having a toplevel class named Store
will hit this ruby 2.5.0 bug https://bugs.ruby-lang.org/issues/14407
That's because of the following buggy behavior of 'defined?' under ruby
2.5:
```
$ ruby -v
ruby 2.5.0p0 (2017-12-25 revision 61468) [x86_64-linux]
$ irb
> class Redis
> end
=> nil
> class Store
> end
=> nil
> defined?(::Redis::Store)
=> "constant"
> ::Redis::Store
NameError (uninitialized constant Redis::Store
Did you mean? Store)
```
