TrivialAccessors breaks methods with ?

[ptarjan]

class Bar
  def self.foo?
    @foo
  end
end

$ rubocop /tmp/a.rb -a

gives

class Bar
  class << self
    attr_reader :foo?
  end
end

which is invalid:

$ ruby /tmp/a.rb
/tmp/a.rb:3:in `attr_reader': invalid attribute name `foo?' (NameError)
        from /tmp/a.rb:3:in `singleton class'
        from /tmp/a.rb:2:in `<class:Bar>'
        from /tmp/a.rb:1:in `<main>'

[Drenmi]

I just tried this out, and can confirm it only happens with class methods. The following is marked as an offense, but not auto-corrected:

class Foo
  def bar?
    @bar
  end
end

[ptarjan]

@Drenmi why is that an offense?

[Drenmi]

@ptarjan: The style guide favours the use of attr_reader. Of course you can't do attr_reader :bar?, because it will try to create an instance variable called @bar?, and question marks are not valid in variable names. It looks like the cop doesn't fully take this into account.

An example of a working way would be:

class Foo
  attr_reader :bar
  alias_method :bar?, :bar
end

[ptarjan]

I thought alias_method as frowned upon? Well whatever works, I just want the rubocop -a to create code that doesn't have syntax errors and is semantically equivalent to the original.

[alexdowad]

Just configure Style/TrivialAccessors with AllowPredicates: true.

(Maintainers, what would you think about making AllowPredicates: true the default? Personally, I prefer it.)

This issue can be closed.

[ptarjan]

Thanks @alexdowad. Where is that option documented? Can you add a little blurb to https://github.com/bbatsov/rubocop/blob/master/config/default.yml

[alexdowad]

Where is that option documented?

RuboCop is, for the most part, not documented. It's a WIP, and a lot of help is needed to finish it.

[ptarjan]

@alexdowad This is similarly broken for writers that don't match the exact pattern.

    def self.email_from(email)
      @email_from = email
    end

Can't be written with attr_writter because it doesn't have the =

[alexdowad]

Let's close this issue. It is resolved using an existing config option.

[ptarjan]

@alexdowad what existing config option? If I set AllowPredicates: true it still complains about #2763 (comment)

[alexdowad]

This is similarly broken for writers that don't match the exact pattern.

The cop wants you to write methods like this using a =.

The original issue here was: "TrivialAccessors breaks methods with ?". That issue is resolved using AllowPredicates.