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There are several situations where I'd like to apply a block to a certain value and use the value inside this block, to use the enumerator coding style to every element.

If such method would be called decompose, it would look like:

result = [3, 4, 7, 8].decompose{ |array| array[2] + array[3] } # result = 15

# OR

result = {:key1 => 'value', :key2 => true}.decompose{ |hash| hash[:key1] if hash[:key2] } # result = 'value'

# OR

[min, max] = [3, 4, 7, 8].decompose{ |array| [array.min, array.max] } # [min, max] = [3, 8]

#  OR

result = 100.decompose{ |int| (int - 1) * (int + 1) / (int * int) } # result = 1

# OR

result = 'Paris'.decompose{ |str| str.replace('a', '') + str[0] } # result = 'PrisP'
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  • Maybe you should include the output, too. Commented Oct 15, 2014 at 9:24
  • This has been asked before but I can't find the question ... Commented Oct 15, 2014 at 9:26
  • Been adding the outputs. Thought it was straightforward. I'm sure something exists (or could easily be monkeypatched to every class) but I can't find it myself either... Commented Oct 15, 2014 at 9:29

2 Answers 2

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The method simply yields self to the block, returning the block's result. I don't think it exists, but you can implement it yourself:

class Object
  def decompose
    yield self
  end
end

[3, 4, 7, 8].decompose{ |array| array[2] + array[3] }
#=> 15

{:key1 => 'value', :key2 => true}.decompose{ |hash| hash[:key1] if hash[:key2] }
#=> "value"

[3, 4, 7, 8].decompose{ |array| [array.min, array.max] }
#=> [3, 8]
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6 Comments

The tap Object method almost does that...
And this post refers to it too: stackoverflow.com/questions/26378890/…
Is it me or you've just posted your own question as a reference in the comment of the answer of your question referring to your question again which is mentioned by you in your comment as a reference to your own question and so on..?
Ok I realize now the mistake. :) I wanted to say that the question is related to this one: stackoverflow.com/questions/7878687/…
@AugustinRiedinger not really, tap returns the object, not the result of the block.
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It actually exists (I could not believe it didn't).

It is called BasicObject#instance_eval. Here's the doc: http://apidock.com/ruby/BasicObject/instance_eval

Available since Ruby 1.9 as this post explains: What's the difference between Object and BasicObject in Ruby?

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5 Comments

instance_eval does much more, it evaluates the block within the context of the receiver.
What does it mean? At least it does exactly what I was looking for!
Take a look at the example in the docs. instance_eval lets you inspect (and modify) the receiver's internal state.
Which the yield self doesn't?
No it doesn't. It just passes the receiver to the block.

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