rails/rails — pull request #7645 by LarryLv (2012-09-14 19:39:10+00:00)
Title: set up config_accessor with a default value by block

* ActiveSupport::Configurable should allow config_accessor to take
default value by block, just like cattr_accessor.

```
class User
include ActiveSupport::Configurable
config_accessor :hair_colors do
[:brown, :black, :blonde, :red]
end
end
```

User.hair_colors # => [:brown, :black, :blonde, :red]

* remove trailing whitespaces in configurable.rb and its test file.

It's an old pull request #5730, but no one implement it . I just implement it like someone suggested, change the interface to just like `cattr_accessor`.