Module: TypeToolkit::DSL

Defined in:
lib/type_toolkit/dsl.rb

Overview

@requires_ancestor: MethodDefRecorder

Instance Method Summary collapse

Instance Method Details

#abstract(method_name) ⇒ Object

Mark method_name as abstract.

A real implementation of the method must be provided somewhere in the ancestor chain. Calls to an unimplemented abstract method will raise AbstractMethodNotImplementedError.

: (Symbol) -> Symbol



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# File 'lib/type_toolkit/dsl.rb', line 13

def abstract(method_name)
  #: self as (Module[top] & HasAbstractMethods & MethodDefRecorder)

  recorded_method_name, is_singleton_method = __last_method_def

  if recorded_method_name != method_name
    prefix = is_singleton_method ? "." : "#"

    # Do not rely on this message content! Its content is subject to change.
    raise <<~MSG.chomp
      `abstract` expected to see `#{prefix}#{method_name}`, but the last recorded method was called `#{recorded_method_name}`.
      This can happen when `abstract` is combined with other metaprogramming.
      If you think this is a bug, please open an issue: https://github.com/Shopify/type_toolkit/issues
    MSG
  end

  # The `method_owner` is the class whose method table stores the abstract method.
  #
  # Example:
  #
  #   class Foo
  #     # is_singleton_method = false, owner is the `Foo` class
  #     abstract def foo; end
  #
  #     # is_singleton_method = true, owner is `Foo.singleton_class`
  #     abstract def self.foo; end
  #   end
  method_owner = is_singleton_method ? singleton_class : self #: as Module[top] & HasAbstractMethods

  # Register the fact that this method is meant to be abstract,
  # used by APIs like `abstract_method_declared?` and `Method#abstract?`
  method_owner.__register_abstract_method(method_name)

  # We never want the empty "stub" method to be called, so we remove it. This has one of 3 effects:
  #
  # 1. If the abstract method is implemented by a subclass, then there's no effect.
  #    The subclass' implementation will always be invoked, so this removal does nothing.
  #
  # 2. If the abstract method was already implemented by a superclass,
  #    Then this removal ensures that calls to the method will resolve to
  #    the superclass' implementation, and never the empty stub.
  #
  # 3. If the abstract method was not implemented anywhere in the ancestor chain,
  #    then this removal ensures we hit `method_missing`, which will then raise
  #    the `AbstractMethodNotImplementedError`.
  method_owner.remove_method(method_name)

  # Return the method name, so `abstract` can be chained, e.g. `private abstract def foo; end`
  method_name
end