There is a ruby style guide by `bbatsov` which [says](https://github.com/bbatsov/ruby-style-guide#source-code-layout):

> Prefer a single-line format for class definitions with no body.

```ruby
# bad
class FooError < StandardError
end

# okish
class FooError < StandardError; end

# good
FooError = Class.new(StandardError)
```

I prefer the second format, what do you think?