Error when trying to have a parent class initialize a child class using `self`

application_interfaces.cr

# Code

abstract class Interface

  def initialize(@application : Application)
  end

  abstract def call

end

class Interface::CommandLine < Interface

  def call
    puts "Running application through the command-line interface." if @application.verbose
  end

end

class Interface::Graphical < Interface

  def call
    puts "Running application through the graphical interface." if @application.verbose
  end

end

class Application

  def self.call(interface_class)
    new(interface_class).call
  end

  def initialize(interface_class : Interface.class)
    @interface = interface_class.new(self)
  end

  getter verbose : Bool = true
  getter! interface : Interface

  delegate call, to: @interface

end

Application.call(Interface::CommandLine)


# Error:
#
#     Error in examples/app_problem.cr:45: instantiating 'Application:Class#call(Interface::CommandLine:Class)'
#
#     Application.call(Interface::CommandLine)
#                ^~~~
#
#     in examples/app_problem.cr:31: instantiating 'Application#call()'
#
#        new(interface_class).call
#                             ^~~~
#
#     in examples/app_problem.cr:41: expanding macro
#
#      delegate call, to: @interface
#      ^
#
#     in macro 'delegate' /usr/local/Cellar/crystal-lang/0.23.1_3/src/object.cr:1067, line 3:
#
#       1.
#       2.       def call(*args, **options)
#     >  3.         @interface.call(*args, **options)
#       4.       end
#       5.
#       6.       def call(*args, **options)
#       7.         @interface.call(*args, **options) do |*yield_args|
#       8.           yield *yield_args
#       9.         end
#      10.       end
#      11.
#      12.
#
#     undefined method 'call' for Nil (compile-time type is (Interface | Nil))
#     Error: 'self' was used before initializing instance variable '@interface', rendering it nilable
#
#     Rerun with --error-trace to show a complete error trace.