button.cr

class Button < BaseComponent
  enum Size
    Small
    Medium
    Large
  end
  needs size : Size = Medium
  
  def render
    with_defaults class: "my button classes #{size_classes}" do |button_builder|
      yield button_builder
    end
  end
  
  def size_classes
    case size
    when Small
      "px-2 py-1"
    # etc.
    end
  end
end

m Button, size: :large, &.link("foo", Foo::Index)

Here's an example version that's Tailwind-specific, but shows a more compiler-ready example:
Definition: https://github.com/stephendolan/lucky_jumpstart/blob/master/src/components/ui/button.cr
Use: https://github.com/stephendolan/lucky_jumpstart/blob/master/src/components/shared/navbar.cr

Nice! Thanks @stephendolan