How to Make the Class Constructor Private in Ruby

How to make the class constructor private in Ruby?

Try this:

class A
  private_class_method :new
end

More on APIDock

Ruby class initialize (constructor) is private method or public method?

Let's see:

class Test
  def initialize; end
end

p Test.new.private_methods.sort.include?(:initialize)

This prints true, so initialize is a private method. This makes sense, it is only called by the new class method if the object is created. If we want, we can do something like this:

class Test
  def initialize
    @counter = 0
  end

  def reset!
    initialize
  end
end

Misusing the constructor like this could however lead to problems if it does more than simple variable initialization.

Want to instantiate a ruby class using a private constructor from factory

Update: Answer

Including this module in my class, protects Klass.new from being called:

module ProtectedConstructor
  def self.included(klass)
    klass.module_eval do
      class << self
        protected :new

        def inherited(klass)
          klass.module_eval do
            def self.new(*args); super; end
          end
        end
      end
    end
  end
end

Instantiating Klass via protected constructor, takes place as such:

Klass.send(:new, *params...*)

Credit for this solution can be found: here

Have a different public constructor than a private one

I guess this would do what you expect.

class C
  def initialize(x, y = 0)
    @x = x
    @y = y
  end

  def self.with_position
    new(3, 4)
  end
end

c1 = C.new(5)
c2 = C.with_position

If you want to prohibit setting y by anyone from outside the class, you can use some private method behind the scenes (as you suggested) and konstructor gem

class C
  def initialize(x)
    set_coords(x, 0)
  end

  konstructor
  def with_position
    set_coords(3, 4)
  end

  private

  def set_coords(x, y)
    @x = x
    @y = y
  end
end

c1 = C.new(5)
c2 = C.with_position

hide ruby's constructor from outsiders but use it inside instance methods

did you try to use send?

SomeClass.send :new, @hash.merge({a => b})

How do I make a class whose constructor looks like the constructor of a built-in class?

class Dog
  def initialize(name)
    @name = name
  end

  def greet
    puts 'hello'
  end
end

def Dog(x)
  Dog.new(x)  #Create a new instance of the Dog class and return it.
end

d = Dog("Rover")
d.greet

--output:--
hello

Ruby factory method to call private setter

This is possible only with a hacky approach:

class Foo
  def self.from_bar(bar)
    new(bar.foo_id).tap { |f| f.send(:bar=, bar) }
    # or, better:
    new(bar.foo_id).tap { |f| f.instance_variable_set(:@bar, bar) }
  end

  private
  attr_accessor :bar
end

Honestly, making attr_accessor private makes a little sense, though.

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