Why default_attributes not being merged with passed attributes in Dry::Struct?

Support
1

Hi!

Recently I started using Dry::Struct and face weird behaviour for example with class:

class MyStruct < Dry::Struct
  attribute :qwe, Types::String.default('qwe')
  attribute :data do
    attribute? :foo, Types::Bool.default(false)
    attribute :bar, Types::Array.default([].freeze)
  end
end

And here is confusion on initialize:

MyStruct.new => # {qwe: 'qwe',data: {foo: false, bar: []}}
MyStruct.new(qwe: 'asd') => # {qwe: 'asd', data: nil}

Digging code founded that default_attributes are being used only when no attributes passed.

Is it intended?
Why not just simple merge?

2

Performance impact would be the first answer.
I’m not sure why MyStruct.new even works, in my understanding it shouldn’t. Besides, combining attribute? with .default is a no-op. Finally, structs defined with inline syntax cannot be made default, the right way would be

class MyStruct < Dry::Struct
  attribute :qwe, Types::String.default('qwe')
  class Data < Dry::Struct
    attribute :foo, Types::Bool.default(false)
    attribute :bar, Types::Array.default([].freeze)
  end
  attribute :data, Data.default { Data.new }
end
3

Got it, thank you!