Ruby: shorter way to define instance variables

Question

I'm looking for the shorter way to define instance variables inside the initialize method:

class MyClass
  attr_accessor :foo, :bar, :baz, :qux
  # Typing same stuff all the time is boring
  def initialize(foo, bar, baz, qux)
    @foo, @bar, @baz, @qux = foo, bar, baz, qux
  end
end

Does Ruby have any in-build feature which lets to avoid this kind of monkey job?

# e. g.
class MyClass
  attr_accessor :foo, :bar, :baz, :qux
  # Typing same stuff all the time is boring
  def initialize(foo, bar, baz, qux)
    # Leveraging built-in language feature
    # instance variables are defined automatically
  end
end

Sergio Tulentsev · Accepted Answer · 2016-03-04 15:18:21Z

10

Meet Struct, a tool made just for this!

MyClass = Struct.new(:foo, :bar, :baz, :qux) do
  # Define your other methods here. 
  # Initializer/accessors will be generated for you.
end

mc = MyClass.new(1)
mc.foo # => 1
mc.bar # => nil

I often see people use Struct like this:

class MyStruct < Struct.new(:foo, :bar, :baz, :qux)
end

But this results in one additional unused class object. Why create garbage when you don't need to?

edited Mar 4, 2016 at 15:18

answered Mar 4, 2016 at 9:53

Sergio Tulentsev

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9 Comments

Ganesh Kunwar Over a year ago

What is the advantage of defining class with this way?

Ganesh Kunwar Over a year ago

I mean the way that you are using in your answer.

Sergio Tulentsev Over a year ago

There are two ways in my answer.

Ganesh Kunwar Over a year ago

First way in your answer.

Sergio Tulentsev Over a year ago

@Stefan: it's a common mis-usage, so I thought I'd warn not to do it :)

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