Memoize helper method instances with Singleton module

Some helpers, like Rails console's `app`, requires memoization of the helper's ivars. To support it IRB needs to memoize helper method instances as well.

Author: st0012

lib/irb/helper_method/base.rb

@@ -1,6 +1,10 @@
+require "singleton"
+
 module IRB
  module HelperMethod
  class Base
+ include Singleton
+
  class << self
  def description(description = nil)
  @description = description if description

lib/irb/workspace.rb

@@ -179,7 +179,7 @@ module HelpersContainer
  def self.install_helper_methods
  HelperMethod.helper_methods.each do |name, helper_method_class|
  define_method name do |*args, **opts, &block|
- helper_method_class.new.execute(*args, **opts, &block)
+ helper_method_class.instance.execute(*args, **opts, &block)
  end unless method_defined?(name)
  end
  end

test/irb/test_helper_method.rb

@@ -97,13 +97,38 @@ def execute
  RUBY
 
  output = run_ruby_file do
- type <<~INPUT
- my_helper
- INPUT
+ type "my_helper"
  type "exit"
  end
 
  assert_include(output, 'Hello from MyHelper')
  end
+
+ def test_helper_method_instances_are_memoized
+ write_ruby <<~RUBY
+ require "irb/helper_method"
+
+ class MyHelper < IRB::HelperMethod::Base
+ description "This is a test helper"
+
+ def execute(val)
+ @val ||= val
+ end
+ end
+
+ IRB::HelperMethod.register(:my_helper, MyHelper)
+
+ binding.irb
+ RUBY
+
+ output = run_ruby_file do
+ type "my_helper(100)"
+ type "my_helper(200)"
+ type "exit"
+ end
+
+ assert_include(output, '=> 100')
+ assert_not_include(output, '=> 200')
+ end
  end
 end