How to chain methods in ruby passing the output of one method to consecutive methods

Question

How can I pass the results of a method to another method in ruby? eg:

class D
  def initialize(text)
    @text = text
  end

  def a s
    "hello #{s}"    
  end

  def b s
    "hi #{s}"
  end
end

So, what I want to do is pass the output of method a to method b. So essentially(if the methods aren't inside a class) I can do the following the following:

puts b(a "Tom") #=>hi hello Tom

However, even if this isn't inside a class, it wouldn't look good if there are a lot of methods so there must be a more elegant way to do this. So what is the proper way to get the output hi hello Tom by applying the methods a and b to an instance of the class D?

UPDATE I just wanted to make it a little bit more clear. Eg, in F# you can do something like this:

let a s = "hello " + s
let b s = "hi " + s
"Tom" |> a |> b #=> hello hi Tom

Here we defined functions a and b and then passed on the results to the next function. I know that its a functional language so ways of doing things would be different there. But I am just wondering if there are any such tricks in Ruby?

“so there must be a more elegant way to do this”—why is that? One might use puts b a 'Tom', but I doubt it’s “more elegant.” — Aleksei Matiushkin
– Aleksei Matiushkin, Commented Nov 23, 2016 at 13:10
The question remains: why on the Earth you think that F#’s way is more elegant? — Aleksei Matiushkin
– Aleksei Matiushkin, Commented Nov 23, 2016 at 13:30

Eric Duminil · Accepted Answer · 2016-11-26 21:52:57Z

6

You can leave the ()

def a s
  "hello #{s}"
end

def b s
  "hi #{s}"
end

puts b a "Tom"

If you have many methods :

puts [:a,:b].inject("Tom"){|result,method| self.send(method,result)}

If you want to use those methods with any object (including Classes) :

module Kernel
  def chain_methods(start_value, *methods)
    methods.inject(start_value){|result,method| self.send(method,result)}
  end
end

class D
  def a s
    "hello #{s}"
  end

  def b s
    "hi #{s}"
  end
end

class E
  class << self
    def a s
      "hello #{s}"
    end

    def b s
      "hi #{s}"
    end
  end
end


# Example with instance methods
puts D.new.chain_methods("Tom", :a, :b)

# Example with class methods
puts E.chain_methods("Tom", :a, :b)

# Thanks mudasobwa :
E.chain_methods("Tom", :a, :b, :puts)

edited Nov 26, 2016 at 21:52

answered Nov 23, 2016 at 13:12

Eric Duminil

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5 Comments

Aleksei Matiushkin Over a year ago

Yay, upvoted for puts [:a,:b].inject("Tom"){|result,method| Object.send(method,result)} :) puts could be chained too, btw.

B A Over a year ago

Wow, this is great! thanks Eric. Now, how can I get the same result if the methods are inside a class, in my example lets say class D, so how can I get the result by applying methods to an instance of class D? Or should I instead use class methods for that?

Lukas Baliak Over a year ago

@BA you can define instance by d = D.new("test") and call d.send instead of Object.send

Jörg W Mittag Over a year ago

Why do you send the methods to Object? In the original code, they are sent to self, so you are calling completely different method. Although, please use public_send instead, there's no reason to break encapsulation here.

Eric Duminil Over a year ago

I wanted the code to also work when a and b are defined in main, since the OP mentioned it. In that case, they are private methods, available to every object.

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