When using IRB, you have surely noticed that after each expression, Ruby prints the result of that expression:

2 + 2
# => 4

"Hello, world!"
# => "Hello, world!"

[1, 2, 3].map { |x| x * 2 }
# => [2, 4, 6]

{ a: 1, "b" => 2 }
# => {a: 1, "b" => 2}

class User
  attr_reader :name

  def initialize(name)
    @name = name
  end
end

User.new("Sam")
# => #<User:0x00007f9c8b0c8d8 @name="Sam">
    

But have you ever wondered how Ruby decides what to print? The answer is that Ruby calls the #inspect method on the resulting object to get a string representation of it.

By overriding #inspect in our classes, we can customize how instances of those classes are displayed:

class User
  attr_reader :name

  def initialize(name)
    @name = name
  end

  def inspect
    "👤 #{@name}"
  end
end

User.new("Sam")
# => 👤 Sam
    

This is especially useful for big objects where the default #inspect output can be overwhelming.

Other situations where #inspect is invoked include passing objects into the p and pp methods, which are intended for debugging output.

History

Object#inspect has been part of Ruby since its inception.