How to generate initializer in Ruby?

Question

It's time to make it shorter:

class Foo
  attr_accessor :a, :b, :c, :d, :e

  def initialize(a, b, c, d, e)
    @a = a
    @b = b
    @c = c
    @d = d
    @e = e
  end
end

We have 'attr_accessor' to generate getters and setters.

Do we have anything to generate initializers by attributes?

Answer 1

Easiest:

Foo = Struct.new( :a, :b, :c )

Generates both accessors and initializer. You can further customize your class with:

Foo = Struct.new( … ) do
  def some_method
    …
  end
end

Answer 2

We can create something like def_initializer like this:

# Create a new Module-level method "def_initializer"
class Module
  def def_initializer(*args)
    self.class_eval <<END
      def initialize(#{args.join(", ")})
        #{args.map { |arg| "@#{arg} = #{arg}" }.join("\n")}
      end
END
  end
end

# Use it like this
class Foo
  attr_accessor   :a, :b, :c, :d
  def_initializer :a, :b, :c, :d

  def test
    puts a, b, c, d
  end
end

# Testing
Foo.new(1, 2, 3, 4).test

# Outputs:
# 1
# 2
# 3
# 4