Interesting quirk with Structs in Transproc

hash_spec.rb

# spec/integration/hash_spec.rb

describe 'combining transformations' do
  it 'applies functions to a struct' do
    symbolize_keys = Transproc(:symbolize_keys)
    map = Transproc(:map_hash, user_name: :name, user_email: :email)

    transformation = symbolize_keys + map

    InputUser = Struct.new(:user_name, :user_email)
    input = InputUser.new('Jade', '[email protected]')

    output = { name: 'Jade', email: '[email protected]' }

    result = transformation[input]

    expect(result).to eql(output)
  end
end

results

Failures:

  1) Hash mapping with Transproc combining transformations applies functions to a struct
     Failure/Error: result = transformation[input]
     ArgumentError:
       odd number of arguments for Hash
     # ./lib/transproc/hash.rb:3:in `[]'
     # ./lib/transproc/hash.rb:3:in `block in <module:Transproc>'
     # ./lib/transproc/function.rb:16:in `[]'
     # ./lib/transproc/function.rb:16:in `block in compose'
     # ./lib/transproc/function.rb:11:in `[]'
     # ./lib/transproc/function.rb:11:in `call'
     # ./spec/integration/hash_spec.rb:157:in `block (3 levels) in <top (required)>'

Finished in 0.06424 seconds (files took 1.66 seconds to load)
52 examples, 1 failure

This is expected behaviour. Only hashes are fully supported. Structs just happen to work in some cases because they declare the [] method as an alternative way of accessing attributes.