Ruby code explanation

Question

I found following code at the internet

class Test
  def value
    'string'
  end

  def inspect
    'value'
  end
end

def test(arg)
  arg.tap { |i| i.value }
end

p test(Test.new)

Could anyone explain why it returns

p test(Test.new) 
# >> value

It's because method `test` ultimately returns `Test` instance, on which method `inspect` is called (internally, by Ruby console) to display it on the screen. — Marek Lipka, Feb 10 '18 at 09:38
"returns" or "prints"? Big difference. This code __returns__ a `Test`, but it __prints__ string `"value"`. — Sergio Tulentsev, Feb 10 '18 at 10:12
Please, read "[How to handle “Explain how this ${code dump} works” questions](https://meta.stackoverflow.com/a/253896/2988)". — Jörg W Mittag, Feb 10 '18 at 14:30

score 1 · Accepted Answer · edited Feb 10 '18 at 15:04

1

Because arg.tap returns arg itself, and p prints arg.inspect, since you have overwritten theinspect method of Test, it returns a string 'value', so you the print result is value

see also:
- p vs puts in Ruby
- tap method

edited Feb 10 '18 at 15:04

mikej

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answered Feb 10 '18 at 09:57

Fangxing

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score 1 · Answer 2 · answered Feb 10 '18 at 11:54

1

tap used for chain of methods. It runs the passed blocked and returns the input without any change.

It means

arg.tap { |i| i.value } will return arg

p method runs inspect method of passed object

answered Feb 10 '18 at 11:54

Mohsen Alizadeh

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Ruby code explanation

2 Answers2