Question

I’m fairly sure that’s a useless title… sorry.

I want to be able to pass in a Class to a method, and then use that class. Here’s an easy, working, example:

def my_method(klass)
  klass.new
end

Using that:

>> my_method(Product)
=> #<Product id:nil, created_at: nil, updated_at: nil, price: nil>
>> my_method(Order)
=> #<Order id:nil, created_at: nil, updated_at: nil, total_value: nil>

What doesn’t work is trying to use the klass variable on a module:

>> ShopifyAPI::klass.first
=> NoMethodError: undefined method `klass' for ShopifyAPI:Module

Am I attempting an impossible task? Can anyone shed some light on this?

Cheers

Answer 1

First off, I don’t think this is impossible.

Surely, there is no klass method defined for modules <- this is true because ShopifyAPI.methods.include? "klass" # => false

However, classes are constants in modules. And modules have a constants method that you may use to retrieve classes. The problem with this is method is that is also retrieves constants in the modules that are not classes.

I came up with this workaround for your problem

# get all the classes in the module
klasses = ShopifyAPI.constants.select do |klass|
    ShopifyAPI.const_get(klass).class == Class
end

# get the first class in that list
klasses.first