Shaped Ruby Struct

shaped_struct.rb

# frozen_string_literal: true
# This class creates a object which behaves like a hash, except that it also
# responds to hash keys sent as messages. We need this type for GraphQL
# because the Gem sends messages to our objects instead of accessing it with
# `:[]`.
#
# It also performs type checking based on a type provided to the shape:
#
# === Example ===
#
# test_case = ShapedStruct.from_hash({
#   books: {
#     codes: [String, Integer, {
#       description: String

#     }]
#   }
# }, {
#   books: {
#     codes: ['123', 1234, {
#       description: 'some type'
#     }]
#   }
# })
#
module ShapedStruct
  # Creates a new ShapedStruct class
  def self.from_hash(shape, hash)
    new_hash = shape.map do |key, value|
      new_value = case value
                  when Hash
                    from_hash(value, hash[key])
                  when Array
                    from_array(value, hash[key])
                  else
                    # key here is a type, check if the type is the same as the value
                    unless value === hash[key]
                      raise "Wrong format supplied, expected #{hash[key]} to be of type #{value}"
                    end
                    hash[key]
                  end
      [key, new_value]
    end.to_h

    the_type = Struct.new(*shape.keys)

    values_to_set = shape.keys.map do |key|
      new_hash[key]
    end

    the_instance = the_type.new(*values_to_set)

    the_instance
  end

  def self.from_array(shape, arr)
    if shape.length != arr.length
      raise "Shape length of length #{shape.length} does not match array of length #{shape.length}"
    end

    shape.zip(arr).map do |key, value|
      case key
      when Hash
        from_hash(key, value)
      when Array
        from_array(key, value)
      else
        # key here is a type, check if the type is the same as the value
        unless key === value
          raise "Wrong format supplied, expected #{value} to be of type #{key}"
        end
        value
      end
    end
  end
end

### Test cases

# test_case = ShapedStruct.from_hash({
#   books: String
# }, {
#   books: 'some string'
# })

# puts test_case.books

# will raise
# test_case = ShapedStruct.from_hash({
#   books: Integer
# }, {
#   books: 1
# })

# puts test_case.books

# test_case = ShapedStruct.from_hash({
#   books: {
#     code: String
#   }
# }, {
#   books: {
#     code: '123'
#   }
# })

# puts test_case.books.code # 123

# test_case = ShapedStruct.from_hash({
#   books: {
#     codes: [String, Integer]
#   }
# }, {
#   books: {
#     codes: ['123', 1234]
#   }
# })

# a = test_case.books.codes
# puts a[0] # 123

# test_case = ShapedStruct.from_hash({
#   books: {
#     codes: [String, Integer, {
#       description: String

#     }]
#   }
# }, {
#   books: {
#     codes: ['123', 1234, {
#       description: 'some type'
#     }]
#   }
# })

# puts test_case.books.codes[2].description # some type