Ruby Pattern Matching

pattern_matching.rb

class Response
  attr_reader :status, :data

  def initialize(status, data)
    @status = status
    @data = data
  end

  def deconstruct
    by_status
  end

  def deconstruct_keys(_keys)
    by_status
  end

  private
  def by_status(ok: nil, error: nil, not_found: nil)
    case @status
    when 200
      ok || { ok: @data }
    when 404
      not_found || { error: "File not found" }
    else
      error || {error: @data }
    end
  end
end

data = { one: "two", three: "four" }

case Response.new(200, data)
in ok: result
  puts "Success: #{result}"
in error: reason
  puts "Error: #{reason}"
end
#=> "Success:  { one: "two", three: "four" }"


case Response.new(403, "Something went wrong")
in ok: result
  puts "Success: #{result}"
in error: reason
  puts "Error: #{reason}"
end
# => "Error: Something went wrong"

case Response.new(404)
in ok: result
  puts "Success: #{result}"
in error: reason
  puts "Error: #{reason}"
end
# => "Error: File not found"

wrapping_an_api_custom_class.rb

# Imagine that you get a custom class returned from an API

ApiCustomResponseClass =
  Struct.new(:status, :body, :message, keyword_init: true) do
    def success?
      status == 200
    end
  end

# It probably does not have #deconstruct or #deconstruct_keys so this Response class acts as a helpful wrapper.
class Response
  attr_reader :status, :data

  def initialize(res)
    @status = res.status
    @data = res.success? ? res.body : res.message
  end

  def deconstruct
    by_status
  end

  def deconstruct_keys(_keys)
    by_status
  end

  private

  def by_status(ok: nil, error: nil, not_found: nil)
    case @status
    when 200
      { ok: @data }
    else
      { error: @data }
    end
  end
end

successful_response =
  ApiCustomResponseClass.new(
    { status: 200, body: { one: "two", three: "four" } }
  )
failed_response =
  ApiCustomResponseClass.new({ status: 403, message: "Unauthorized" })
not_found_response =
  ApiCustomResponseClass.new({ status: 404, message: "File Not Found" })

[successful_response, failed_response, not_found_response].each do |res|
  case Response.new(res)
  in ok: result
    puts "Success: #{result}"
  in error: reason
    puts "Error: #{reason}"
  end
end