How can I call a class method in Ruby with the method name stored in an array?

Question

I am currently working on a Poker game in Ruby. Instead of using numerous if-else statements to check the value of the player's hand, I decided to do the following:

  #calculate the players score
  def score
    POSS.map {|check|
      if (check[1].call())
        @score = check[0]
        puts @score
        return check[0]
      else
        false
      end
    }
  end

      POSS = [
    [10, :royal_flush?],
    [9, :straight_flush?],
    [8, :four_kind?],
    [7, :full_house?],
    [6, :flush?],
    [5, :straight?],
    [4, :three_kind?],
    [3, :two_pairs?],
    [2, :pair?]
  ]

The second item in each item of 'POSS' is a method I created to check whether the player has that hand. I am attempting to call the method with .call(), but get the following error:

Player.rb:43:in `block in score': undefined method `call' for 
:royal_flush?:Symbol (NoMethodError)    from Player.rb:42:in `map'  from
Player.rb:42:in `score'     from Player.rb:102:in `get_score'   from
Player.rb:242:in `<main>'

Schylar · Accepted Answer · 2015-07-18T04:05:19.813

http://ruby-doc.org/core-2.2.2/Object.html Object#send is the method you are looking for.

Since you are wanting a 'class method', then Object should be self when declaring instance methods of the class that contains the 'class methods'

Try this code

 #calculate the players score
  def score
    POSS.map do |check|
      if self.send check[1] 
        @score = check[0]
        puts @score
        return check[0]
      else
        false
      end
    end
  end

      POSS = [
    [10, :royal_flush?],
    [9, :straight_flush?],
    [8, :four_kind?],
    [7, :full_house?],
    [6, :flush?],
    [5, :straight?],
    [4, :three_kind?],
    [3, :two_pairs?],
    [2, :pair?]
  ]

Styles vary from person to person, however, I think when using multi line blocks, it would be best to use 'do,end' pair instead of '{ }'

https://github.com/bbatsov/ruby-style-guide

I think some confusion may come from code that looks like this

foobar = ->(foo,bar){puts "Passed in #{foo}, #{bar}"}
foobar.call("one","two")

If the first line was abstracted into other parts of the program you may have thought that foobar was a method, but its really a lambda. Procs and Lambdas are just like methods but better.. in their own way.. Check out this article on Procs, Blocks and Lambdas.

http://www.reactive.io/tips/2008/12/21/understanding-ruby-blocks-procs-and-lambdas/

But also if interested check out https://www.codecademy.com/forums/ruby-beginner-en-L3ZCI for more detailed hands on with PBLS

Perfect, thank you very much! And thank you for your suggestion and links, I will definitely check those out! — Power Project, Jul 18 '15 at 04:11

score 0 · Answer 2 · edited May 23 '17 at 12:25

0

No method is no method; and there is no Symbol#call which causes the immediate error.

The (or rather, a) way to call is via Object#__send__, supplying the name and arguments. One could also resolve a method and then call that; but __send__ is the most direct route as Ruby is based on message passing.

That is, instead of symbol.call(..), use obj.__send__(symbol, ..). (In this case the object would probably be self.)

See Understanding Ruby symbol as method call

edited May 23 '17 at 12:25

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answered Jul 18 '15 at 03:46

user2864740

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It continues to give me the same error. I have royal_flush? defined earlier and it works when tested individually. Here is what my call looks like with your suggested changes: POSS.map {|check| if (Player.send check[1]) – Power Project Jul 18 '15 at 04:06
@PowerProject No method is no method. If it gives the same error (it will be the same *type* of error, but for a different receiver object and method name) then see previous. A method named `x` has to be present on `obj` when using `obj.__send__(:x)`. In this case you probably don't want to use `Player` (a class), but rather a *particular* player instance. If you do want to use a class, make sure that *class methods* are used. – user2864740 Jul 18 '15 at 04:07
The problem was that I was doing Player.send instead of self.send as mentioned by @Schylar – Power Project Jul 18 '15 at 04:12
@PowerProject See the relevant linked documentation. Such is how `__send__` works. – user2864740 Jul 18 '15 at 04:15

score 0 · Answer 3 · edited Apr 13 '17 at 12:40

0

You can use send.

class Foo
  def self.bar
    "bar"
  end

  def baz
    "baz"
  end
end

Foo.send(:bar) # => "bar"
f = Foo.new
f.send(:baz) # => "baz"

Though I'm not sure this is the best approach for the app you're writing. When you get it working you can post it on CodeReview.

edited Apr 13 '17 at 12:40

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answered Jul 18 '15 at 03:50

jcm

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How can I call a class method in Ruby with the method name stored in an array?

3 Answers3