Ruby 2.5 allows creating structs with keyword arguments

In Ruby, structs can be created using positional arguments.

Customer = Struct.new(:name, :email)
Customer.new("John", "[email protected]")

This approach works when the arguments list is short. When arguments list increases then it gets harder to track which position maps to which value.

Here if we pass keyword argument then we won't get any error. But the values are not what we wanted.

Customer.new(name: "John", email: "[email protected]")
=> #<struct Customer name={:name=>"John", :email=>"[email protected]"}, email=nil>

Ruby 2.5 introduced creating structs using keyword arguments. Relevant pull request is here.

However this introduces a problem. How do we indicate to Struct if we want to pass arguments using position or keywords.

Takashi Kokubun suggested to use keyword_argument as an identifier.

Customer = Struct.new(:name, :email, keyword_argument: true)
Customer.create(name: "John", email: "[email protected]")

Matz suggested to change the name to keyword_init.

So in Ruby 2.5 we can create structs using keywords as long as we are passing keyword_init.

Customer = Struct.new(:name, :email, keyword_init: true)

Customer.new(name: "John", email: "[email protected]")
=> #<struct Customer name="John", email="[email protected]">