Get an argument error in ruby blocks

Question

module Framework
 class CreateTableDefinition 
   attr_accessor :host, :username, :password
 end 
end

def create_table(table_name)
  obj = Framework::CreateTableDefinition.new
  yield(obj) if block_given?
end

create_table :users do |config|
  config.host :localhost
end

And here is the error I get

-:13:in `block in <main>': wrong number of arguments (1 for 0) (ArgumentError)
    from -:9:in `create_table'
    from -:12:in `<main>'

If I change the code to

config.host = :localhost

it works fine. But what I want is to work as described above config.host :localhost

It sounds like you want the CreateTableDefinition class to have a host method that assigns its argument to the @host local, does that sound right? — Andrew
– Andrew, Commented Aug 8, 2014 at 17:21
@AndrewPiliser, correct but I want to ommit the = I spot that most of the RoR code make the assignments like that config.host :localhost. See no = — MZON
– MZON, Commented Aug 8, 2014 at 17:25

BroiSatse · Accepted Answer · 2014-08-08 17:38:11Z

2

You missed assignment:

config.host = :localhost

Edit

If you want to get rid of assignments, you need to define setter methods without = at the end. This might generate quote a lot of code, so I would rather go with some meta-programming (because it's fun!)

class MyConfigClass
  def self.attributes(*args)
    args.each do |attr|
      define_method attr do |value|
        @attributes[attr] = value
      end
    end
  end

  def initialize
    @attributes = {}
  end

  def get(attr)
     @attributes[attr]
  end 
end

class CreateTableDefinition < MyConfigClass
   attributes :host, :username, :password
end

c = CreateTableDefinition.new
c.host :localhost
c.get(:host)   #=> :localhost

edited Aug 8, 2014 at 17:38

answered Aug 8, 2014 at 17:20

BroiSatse

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2 Comments

MZON Over a year ago

I know that but how to do to work with config.host :localhost? I'm learning ruby and notice that most of the RoR blocks make the assignment in that way

BroiSatse Over a year ago

@MZON - I wouldn't say most, rails config uses standard assignments. I'll update the question with how to do that in a second.

Andrew · Accepted Answer · 2014-08-08 17:27:44Z

Try manually making a method that does what you want instead of using the attr_accessor shortcut.

class CreateTableDefinition 
  attr_accessor :username, :password

  def host(sym)
    @host = sym
  end

  def get_host
    @host
  end
end

If you don't like the idea of writing those methods for every attribute, look into writing your own helper, something like attr_rails_like, and mix it in to the Class object. This article might be helpful.

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