Returning two elements: Array vs. Struct

Question

I have a method calculate(data) that returns two values. One is a grade (Float) and another is details (Hash). Comparing the following two options, is there a preferred way?

def calculate(data)
  ...
  [grade, details]
end

grade, details = calculate(data)

vs.

def calculate(data)
  ...
  Result.new(grade, details)
end

result = calculate(data)
grade = result.grade
details = result.details

What is more idiomatic in Ruby?

Answer 1

The array form is more idiomatic. In fact, you can do it via Ruby's built-in multiple returns mechanism:

def calculate(data)
  ...
  return grade, details
end

grade, details = calculate(data)

Answer 2

For a method intended to be used internal to a library, your first option is more efficient and would be a good choice. For a method intended to be used by a user of a library, something along the lines of your second option has more desirable interface, and should be used.