Ruby’s Object#tap is a small but powerful method that often goes unnoticed. It allows you to “tap into” a method chain, perform some operation, and return the original object—regardless of what the block inside returns. This makes it particularly useful for debugging, configuration, or inserting side effects without breaking the flow of your code.

A Simple Use Case: Debugging

Take the following example:

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n = [1,2,3].map { _1 % 2 }.map { _1 * 10 }

This returns [10, 0, 10]. But what if that’s not what you expected? You might want to inspect the result of the first map:

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n = [1,2,3].map { _1 % 2 }
puts n.inspect
n = n.map { _1 * 10 }
puts n.inspect

Using tap, we can make this more elegant:

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n = [1, 2, 3].map { _1 % 2 }
             .tap { puts _1.inspect }
             .map { _1 * 10 }
             .tap { puts _1.inspect }

Output:

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[1, 0, 1]
[10, 0, 10]
=> nil

You achieve the same result, but the code remains tidy and fluent—without breaking the method chain.

How tap Works Internally

The method is implemented in C in Ruby’s source code:

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static VALUE
rb_obj_tap(VALUE obj)
{
    rb_yield(obj);
    return obj;
}

Translated to Ruby, it looks like this:

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class Object
  def tap
    yield self
    self
  end
end

This shows how tap yields the object to the block but always returns the object itself. It doesn’t modify the object unless you explicitly do so inside the block.

Practical Use Cases

1. Debugging (as shown above)

2. Inline Configuration of ActiveRecord Models

Without tap:

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user = User.new(email: "[email protected]")
user.name = 'Harisankar'
user.admin = true if user.email.ends_with?("@example.com")
user.save

With tap:

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user = User.new(email: "[email protected]").tap do |u|
  u.name = "Harisankar"
  u.admin = true if u.email.ends_with?("@example.com")
end.save

3. Building Complex Hashes or Payloads

Before:

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def build_payload
  @build_payload ||= begin
    payload = {}
    payload[:user_id] = current_user.id
    payload[:timestamp] = Time.now.utc
    payload[:signature] = generate_signature(payload)
    payload
  end
end

With tap:

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def build_payload
  @build_payload ||= {}.tap do |payload|
    payload[:user_id] = current_user.id
    payload[:timestamp] = Time.now.utc
    payload[:signature] = generate_signature(payload)
  end
end

4. Cleaner DSLs and Initialization Chains

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MyApp::Setup.new.tap do |config|
  config.enable_caching = true
  config.retry_limit = 3
end.run!

5. Side Effects like Tracking Access

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def fetch_user(id)
  User.find(id).tap do |user|
    user.touch(:last_accessed_at)
  end
end

Conclusion

Ruby’s tap may seem like a tiny utility, but it’s a subtle powerhouse. Whether you’re debugging, configuring objects inline, or composing fluent DSLs, tap keeps your code clean and expressive. It doesn’t change the object unless you explicitly do so, and yet it gives you the flexibility to inspect, mutate, or hook into your logic mid-flow—without breaking your method chains.

Use it wisely, and it can make your Ruby code more readable, elegant, and fun to write.