Is there any reason to use Classname.new keyword in ruby other than when creating an instance of an object in a main

Question

This class takes in a hash, and depending on the input, it converts temperatures.

class Temp
  def initialize(opt={})
    if opt.include?(:cold)
      @colddegree=opt[:cold]
    end
  end
  def self.from_cold(cel)
    Temp.new(:cold => cel) <= instance of class created in class method
  end
end

An instance of a class is created inside a class method. Why is it necessary to do so, and what it does it do, what is the reasoning behind it?

• Why would we need to create an instance of a class inside the class instead of the main?
• Why would it be used inside a class method? Can there be a time when it would be required inside a regular object methods?
• What is it calling and what is happening when it is creating an instance inside a class method? what difference does it make?

Answer 1

Rubyists don't always use the word, but self.from_cold is a factory. This allows you to expose a Temp.from_cold(-40) method signature that programmers consuming your API can understand readily without having to concern themselves with the boilerplate of, say, learning that you have an implicitly required parameter named :cold.

It becomes extra useful when you have a work-performing object that needs to be initialized and then invoked, such as TempConverter.new(cel: -40).to_fahrenheit. Sometimes it's cleaner to expose a TempConverter.cel_to_fahr(-40) option to be consumed by other libraries. It's mostly just a way of hiding complexity inside of this class so that other classes with temp conversion needs don't have to violate the Law of Demeter.