example.rb

require_relative "./interactor"

ctx = SomeInteractor::Context.new(var_a: true)
res = SomeInteractor.new(ctx).call

assert res.success?

res = SomeInteractor.new(var_a: false).call

assert res.failure?

begin
  SomeInteractor.new(var_b: :foo).call
rescue => e
  assert e.present?
end

interactor.rb

class SomeInteractor
  Context = ImmutableStruct.new(:var_a)
  
  attr_reader :context
  
  def initialize(ctx, **opts)
    ctx ||= Context.new(**opts)
    raise unless ctx.is_a?(Context)
    @context = ctx
  end
  
  def call
    return Success(context) if context.var_a
    Failure("context#var_a is falsy")
  end
end