I was watching a youtube video about Ruby Blocks, Procs, and Lambdas and noticed something interesting.

Let’s do this with some Ruby code.

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fruits = ["apple", "orange", "kiwi", "mango", "banana"]

fruits.each do |fruit|
  puts "I like to eat #{fruit}" unless fruit == "kiwi"
end

This is a simple block, and if you don’t feel you understand them because you’re new to Ruby (like me at the time of this writing), you should read this StackOverflow answer.

Let’s add a return to this.

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fruits = %w[apple orange kiwi mango banana]

fruits.each do |fruit|
  puts "I like to eat #{fruit}" unless fruit == "kiwi"
  return "unacceptable" if fruit == "kiwi"
end

The return here works like a break in a traditional loop. It doesn’t really return anything since the each method isn’t returning anything. However, this exits out of the scope that’s using the block. Which means that this return is just exitting out of my script here.

Let’s put this inside a function to make things easier for us to snoop around.

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def main
  fruits = %w[apple orange kiwi mango banana]

  fruits.each do |fruit|
    puts "I like to eat #{fruit}" unless fruit == 'kiwi'
    return fruit if fruit == 'kiwi'
  end
end

fave_fruit = main
puts "I love #{fave_fruit}!"

Here, the method exits after 2 runs, and I get the value of fave_fruit.

The return exits us out of the scope that it’s called it. Quite neat. But I’m certain this is going to trip me up some day so I’m writing it down.

If I were to do this with a Proc:

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def main
  fruits = %w[apple orange kiwi mango banana]

  fruit_proc = Proc.new do |fruit|
    puts "I like to eat #{fruit}" unless fruit == 'kiwi'
    return fruit if fruit == 'kiwi'
  end

  fruits.each(&fruit_proc)
  puts "I've processed all the fruits."
end

fave_fruit = main
puts "I love #{fave_fruit}!"

$ ruby code/posts/ruby-block-return/ex_1.rb
I like to eat apple
I like to eat orange
I love kiwi!

This block does the same thing, with procs. Notice how the puts "I've processed all the fruits." line is not printing.

Let’s try this with a lambda:

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def main
  fruits = %w[apple orange kiwi mango banana]
  fruit_lambda = lambda do |fruit|
    puts "I like to eat #{fruit}" unless fruit == 'kiwi'
    fruit if fruit == 'kiwi'
  end
  fruits.each(&fruit_lambda)
  puts "I've processed all the fruits."
end
fave_fruit = main
puts "I love #{fave_fruit}!" unless fave_fruit.nil?

The output is very different now.

❯ ruby code/posts/ruby-block-return/ex_1.rb
I like to eat apple
I like to eat orange
I like to eat mango
I like to eat banana
I've processed all the fruits.

It doesn’t get the return value fruit if fruit == 'kiwi' at all now.

A lambda is useful when you want to eject only out of the current loop call, not the entire scope that you’re calling this from.

I don’t really have many more observations, but if I do, I’ll write another post.

Other Posts in This Series

• Ruby
• Ruby Blocks
• Some Smalltalk about Ruby Loops
• Symbolic Ruby