DEV Community: Seiei Miyagi

Apply Reference table to the Rails STI type/Polymorphic type/enum/inclusion validated columns

Seiei Miyagi — Sun, 28 Jun 2020 07:19:49 +0000

Applying Reference table¹ to the Rails application by following 2 steps.

Create reference tables that contains STI types / Polymorphic types / possible enum values / inclusion values.
Add foreign key constraint from the column to the reference table to prevent to set a wrong name to STI type / set a wrong name to Polymorphic type / set a invalid value to the enum / set a excluded values to inclusion validated column.

Sample repository

https://github.com/hanachin/iikanji_enum/

How to do

Set same type to a id column of a reference table and type column of a model table, or enum value column of the model table.
Then add foreign key constraint.

Sample migration file is looks like following:

# db/migrate/20200627151958_create_posts.rb
class CreatePosts < ActiveRecord::Migration[6.0]
  def change
    create_table :posts do |t|
      t.string :type
      t.integer :state
      t.string :title
      t.text :body

      t.timestamps
    end

    create_table :post_states do |t|
      t.string :name

      t.timestamps
    end
    add_foreign_key :posts, :post_states, column: :state

    create_table :post_types, id: :string do |t|
      t.timestamps
    end
    add_foreign_key :posts, :post_types, column: :type
  end
end

After a rails db:migrate, the db/schema.rb will looks like following:

# db/schema.rb
# This file is auto-generated from the current state of the database. Instead
# of editing this file, please use the migrations feature of Active Record to
# incrementally modify your database, and then regenerate this schema definition.
#
# This file is the source Rails uses to define your schema when running `rails
# db:schema:load`. When creating a new database, `rails db:schema:load` tends to
# be faster and is potentially less error prone than running all of your
# migrations from scratch. Old migrations may fail to apply correctly if those
# migrations use external dependencies or application code.
#
# It's strongly recommended that you check this file into your version control system.

ActiveRecord::Schema.define(version: 2020_06_27_160353) do

  # These are extensions that must be enabled in order to support this database
  enable_extension "plpgsql"

  create_table "post_states", force: :cascade do |t|
    t.string "name"
    t.datetime "created_at", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false
  end

  create_table "post_types", id: :string, force: :cascade do |t|
    t.datetime "created_at", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false
  end

  create_table "posts", force: :cascade do |t|
    t.string "type"
    t.integer "state"
    t.string "title"
    t.text "body"
    t.datetime "created_at", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false
  end

  add_foreign_key "posts", "post_states", column: "state"
  add_foreign_key "posts", "post_types", column: "type"
end

When there are STI models that uses ActiveRecord::Enum like following:

# app/models/post.rb
class Post < ApplicationRecord
  enum state: { draft: 0, published: 1 }
end

# app/models/draft_post.rb
class DraftPost < Post
end

# app/models/published_post.rb
class PublishedPost < Post
end

Create reference table records that possible values of STI types / enum values like following:

# app/models/post/state.rb
class Post < ApplicationRecord
  class State < ApplicationRecord
    class << self
      def seed
        Post.states.each do |state, id|
          find_or_create_by!(id: id, name: state)
        end
      end
    end
  end
end

# app/models/post/type.rb
class Post < ApplicationRecord
  class Type < ApplicationRecord
    class << self
      def seed
        [PublishedPost, DraftPost].each do |klass|
          find_or_create_by!(id: klass.name)
        end
      end
    end
  end
end

Then run rails runner Post::Type.seed rails runner Post::State.seed.

Once reference tables and foreign key constraint set up, then you can see You can not save the model with type that does not exists on a reference table post_types.

Loading development environment (Rails 6.0.3.2)
irb(main):001:0> post = Post.first
  Post Load (0.2ms)  SELECT "posts".* FROM "posts" ORDER BY "posts"."id" ASC LIMIT $1  [["LIMIT", 1]]
irb(main):002:0> post
=> #<DraftPost id: 3, type: "DraftPost", state: "draft", title: "test", body: "test", created_at: "2020-06-27 16:14:49", updated_at: "2020-06-27 16:14:49">
irb(main):003:0> post.type = "YavayPost"
irb(main):004:0> post.save!
   (0.3ms)  BEGIN
  DraftPost Update (1.2ms)  UPDATE "posts" SET "type" = $1, "updated_at" = $2 WHERE "posts"."id" = $3  [["type", "YavayPost"], ["updated_at", "2020-06-27 16:40:40.492136"], ["id", 3]]
   (0.2ms)  ROLLBACK
Traceback (most recent call last):
        1: from (irb):4
ActiveRecord::InvalidForeignKey (PG::ForeignKeyViolation: ERROR:  insert or update on table "posts" violates foreign key constraint "fk_rails_43c128f7b9")
DETAIL:  Key (type)=(YavayPost) is not present in table "post_types".
irb(main):005:0>

The enum column is also the same, You can not save the enum value that does not exists on a reference table post_states.

Loading development environment (Rails 6.0.3.2)
irb(main):001:0> class Post; enum state: { amasawa: 4423 }; end
=> {:state=>{:amasawa=>4423}}
irb(main):002:0> post = Post.first
  Post Load (0.2ms)  SELECT "posts".* FROM "posts" ORDER BY "posts"."id" ASC LIMIT $1  [["LIMIT", 1]]
irb(main):003:0> post
=> #<DraftPost id: 3, type: "DraftPost", state: nil, title: "test", body: "test", created_at: "2020-06-27 16:14:49", updated_at: "2020-06-27 16:14:49">
irb(main):004:0> post.state = :amasawa
irb(main):005:0> post.save!
   (0.3ms)  BEGIN
  DraftPost Update (1.3ms)  UPDATE "posts" SET "state" = $1, "updated_at" = $2 WHERE "posts"."id" = $3  [["state", 4423], ["updated_at", "2020-06-27 16:43:03.201733"], ["id", 3]]
   (0.2ms)  ROLLBACK
Traceback (most recent call last):
        1: from (irb):5
ActiveRecord::InvalidForeignKey (PG::ForeignKeyViolation: ERROR:  insert or update on table "posts" violates foreign key constraint "fk_rails_93ccb3c476")
DETAIL:  Key (state)=(4423) is not present in table "post_states".
irb(main):006:0>

Conclusion

Database constraint is awesome. Let's use reference table in the Rails apps.

You can apply the Reference table to STI types and possible enum values.
Also You can apply the Reference table to Polymorphic types and valid inclusion values.

https://en.wikipedia.org/wiki/Reference_table ↩

Quine Snake Battle

Seiei Miyagi — Tue, 06 Aug 2019 06:10:24 +0000

I made a multiplayer snake game.
https://github.com/hanachin/quine-snake

telnetで対戦できるQuineなsnake game https://t.co/hYCRTGdtSE pic.twitter.com/aziv7ai6yB
— 𝓜𝓲𝔂𝓪𝓰𝓲 (@hanachin_) August 4, 2019

How to play

Run server (requires ruby 2.7+)

$ ruby snake.rb

Then telnet

$ telnet 127.0.0.1 1234

CircleCI Workflows to rerun flaky RSpec examples

Seiei Miyagi — Wed, 10 Jul 2019 05:45:34 +0000

Here is the overview. The point is separating jobs to run all test and run failed test. That allows you to rerun the failed test only. It could save the time because You don't need to rerun whole test suite, You can rerun just failed ones.

# spec/spec_helper.rb
RSpec.configure do |config|
  config.example_status_persistence_file_path = "spec/examples.txt"
end

# .circleci/config.yml
version: 2.1

executors:
  ruby:
    docker:
      - image: circleci/ruby

jobs:
  test:
    executor: ruby
    steps:
      - checkout
      - run: gem install rspec
      - run: rspec --failure-exit-code=0
      - persist_to_workspace:
          root: .
          paths:
            - '*'

  test_again:
    executor: ruby
    steps:
      - attach_workspace:
          at: ~/project
      - run: gem install rspec
      - run: rspec --only-failures

workflows:
  test:
    jobs:
      - test
      - test_again:
          requires: [test]

The test job run whole test suites, that fail sometimes because of flaky test. But it's ok. I'll rerun the failed tests in the test_again job.

RSpec has example_status_persistence_file_path configuration to store the test result.
In this .circleci/config.yml, I use persist_to_workspace to save the test result of the test job and pass them to the test_again job.

test_again job requires the test job, which means rspec exit successfully whether test passed or not to run the test_again job.

A list of jobs that must succeed for the job to start
https://circleci.com/docs/2.0/configuration-reference/#requires

To do this, pass --failure-exit-code=0 option to rspec command.

c.f. \-\-failure\-exit\-code\ option (exit status) - Command line - RSpec Core - RSpec - Relish

Then the test_again job receives the test result of the test job by attach_workspace and run rspec with --only-failures option to run failed test only..

c.f. Only Failures - Command line - RSpec Core - RSpec - Relish

Sample project

I create an example repository

https://github.com/hanachin/rspec-soumen

It has randomly failing test.

using Module.new {
  refine(Integer) do
    def 冷やしそうめんがうまい?
      self >= 25
    end
  end
}

RSpec.describe '冷やしそうめん' do
  it { is_expected.to be }

  context '気候変動' do
    let(:temperature) { rand(10..40) }

    subject { temperature.冷やしそうめんがうまい? }

    it { is_expected.to be }
  end
end

Then the test failed in test job and test_again job.

https://circleci.com/workflow-run/2cced3b3-59c4-4e3e-9f53-33172388b74b

You can see the test job runs whole test suite, and it failed but marked as success.

https://circleci.com/gh/hanachin/rspec-soumen/6

And the test_again job runs failed test only.

https://circleci.com/gh/hanachin/rspec-soumen/7

You can rerun workflows from failed job.
That time the test_again job passed.

https://circleci.com/workflow-run/09fb370d-bbdd-4648-acba-0bebe5a7bddf

Conclusion

I separate the test jobs to run all test and run failed test.

Result:

If tests failed again in test_again, I don't need to rerun whole test suite, I can rerun just failed ones.
I can rerun failed tests without any changes to the test code like rspec-retry or extending Capybara.default_wait_time or something like that.
I don't need to investigate flaky test, just rerun the failed tests.
I know fixing the flaky test is good but it may take tons of times,
I avoid it.
My failed tests rerun automatically in the test_again job once.
I can chain the test_again_again, test_again_again_again jobs as well 😘
I can take statistics of flaky tests in test_again job, maybe.

Cheers🍻

How to define almost global variable and almost top level method in Rails

Seiei Miyagi — Wed, 05 Jun 2019 15:41:38 +0000

# app/models/application_container.rb
require 'singleton'

class ApplicationContainer
  include Singleton
end

# app/controllers/application_controler.rb
class ApplicationController < ActionController::Base
  delegate_missing_to :container

  cattr_accessor :container, default: ApplicationContainer.instance
end

# app/models/application_record.rb
class ApplicationRecord < ActiveRecord::Base
  self.abstract_class = true

  delegate_missing_to :container

  cattr_accessor :container, default: ApplicationContainer.instance
end

Optimize boot time of ruby CLI tools

Seiei Miyagi — Wed, 29 May 2019 10:18:13 +0000

Create a binstub like following:

#!/usr/bin/env ruby
require 'bootsnap'
gem_name = 'rubocop'
exe_name = 'rubocop'
cache_dir = File.join(ENV['HOME'], '.cache', 'bootsnap', gem_name, exe_name)
Bootsnap.setup(cache_dir: cache_dir, load_path_cache: false, autoload_paths_cache: false)
load Gem.bin_path(gem_name, exe_name)

Gem.bin_path¹ takes two arguments, 1st is name of gem, 2nd is name of executable. You can modify gem_name/exe_name to apply this binstub to other ruby CLI tools.

Without this binstub:

% time rubocop -v
0.70.0
rubocop -v  0.76s user 0.20s system 97% cpu 0.983 total

With this binstub, It takes a little more time at first run:

% time bin/rubocop -v
0.70.0
bin/rubocop -v  1.04s user 0.57s system 98% cpu 1.640 total

But once it runs, the cache is created. Then It becomes much faster:

% time bin/rubocop -v
0.70.0
bin/rubocop -v  0.53s user 0.23s system 79% cpu 0.969 total

You don't need to change any code of ruby CLI tools, Just create a binstub to optimize boot time.

Cheers <3

https://www.rubydoc.info/github/rubygems/rubygems/Gem.bin_path ↩

Using RubyVM::AbstractSyntaxTree.of in pry

Seiei Miyagi — Sat, 04 May 2019 04:27:34 +0000

Put following snippets to ~/.pryrc

unless defined?(SCRIPT_LINES__)
  SCRIPT_LINES__ = {}
end

Pry.config.hooks.add_hook(:before_eval, :"ast<3") do |code, _pry|
  SCRIPT_LINES__["(pry)"] = code.lines
  code
end

It works, yay!

% pry
[1] pry(main)> RubyVM::AbstractSyntaxTree.of(-> { puts :hi })
=> (SCOPE@1:32-1:45
 tbl: []
 args:
   (ARGS@1:32-1:32
    pre_num: 0
    pre_init: nil
    opt: nil
    first_post: nil
    post_num: 0
    post_init: nil
    rest: nil
    kw: nil
    kwrest: nil
    block: nil)
 body: (FCALL@1:35-1:43 :puts (ARRAY@1:40-1:43 (LIT@1:40-1:43 :hi) nil)))
[2] pry(main)>

I also wrote a irb version, including how RubyVM::AbstractSyntaxTree.of uses SCRIPT_LINES__.
https://dev.to/okinawarb/how-can-i-use-rubyvm-abstractsyntaxtree-in-irb-m2k

Enjoy AST!

How can I use RubyVM::AbstractSyntaxTree.of in irb?

Seiei Miyagi — Thu, 25 Apr 2019 13:00:41 +0000

Put following snippets to ~/.irbrc.

unless defined?(SCRIPT_LINES__)
  SCRIPT_LINES__ = {}
end

ast_happier = TracePoint.new(:call) do |tp|
  SCRIPT_LINES__['(irb)'] = tp.binding.local_variable_get(:statements).lines
end
ast_happier.enable(target: IRB::WorkSpace.instance_method(:evaluate))

It works, yay!

% irb
irb(main):001:0> pp RubyVM::AbstractSyntaxTree.of(-> { puts :hi })
(SCOPE@1:35-1:48
 tbl: []
 args:
   (ARGS@1:35-1:35
    pre_num: 0
    pre_init: nil
    opt: nil
    first_post: nil
    post_num: 0
    post_init: nil
    rest: nil
    kw: nil
    kwrest: nil
    block: nil)
 body: (FCALL@1:38-1:46 :puts (ARRAY@1:43-1:46 (LIT@1:43-1:46 :hi) nil)))
=> #<RubyVM::AbstractSyntaxTree::Node:SCOPE@1:35-1:48>

But how does it work?

SCRIPT_LINES__ is used for standard library debug.
https://docs.ruby-lang.org/en/2.6.0/DEBUGGER__.html

Of course there is no documentation.

SCRIPT_LINES__ = {} unless defined? SCRIPT_LINES__ # :nodoc:

https://github.com/ruby/ruby/blob/v2_6_3/lib/debug.rb#L22

In the ast.c, SCRIPT_LINES__ is also used for finding the source code of the proc.

static VALUE
script_lines(VALUE path)
{
    VALUE hash, lines;
    ID script_lines;
    CONST_ID(script_lines, "SCRIPT_LINES__");
    if (!rb_const_defined_at(rb_cObject, script_lines)) return Qnil;
    hash = rb_const_get_at(rb_cObject, script_lines);
    if (!RB_TYPE_P(hash, T_HASH)) return Qnil;
    lines = rb_hash_lookup(hash, path);
    if (!RB_TYPE_P(lines, T_ARRAY)) return Qnil;
    return lines;
}

https://github.com/ruby/ruby/blob/v2_6_3/ast.c#L189-L201

static VALUE
rb_ast_s_of(VALUE module, VALUE body)
{
    VALUE path, node, lines;
    int node_id;
    const rb_iseq_t *iseq = NULL;


    if (rb_obj_is_proc(body)) {
        iseq = vm_proc_iseq(body);


        if (!rb_obj_is_iseq((VALUE)iseq)) {
            iseq = NULL;
        }
    }
    else {
        iseq = rb_method_iseq(body);
    }


    if (!iseq) return Qnil;


    path = rb_iseq_path(iseq);
    node_id = iseq->body->location.node_id;
    if (!NIL_P(lines = script_lines(path))) {
        node = rb_ast_parse_array(lines);
    }
    else if (RSTRING_LEN(path) == 2 && memcmp(RSTRING_PTR(path), "-e", 2) == 0) {
        node = rb_ast_parse_str(rb_e_script);
    }
    else {
        node = rb_ast_parse_file(path);
    }


    return node_find(node, node_id);
}

https://github.com/ruby/ruby/blob/v2_6_3/ast.c#L220-L253

During the RubyVM::AbstractSyntaxTree.of, ruby does

read the file location from the RubyVM::InstractionSequence of given proc.
read whole source code from some sources, such as SCRIPT_LINES__/the real file/command line input given by -e
parse whole source code again to create an AST.
read the node id from the RubyVM::InstructionSequence of given proc.
find a node from the AST, the node which has same node id of given proc.

If parsing the same file, ruby parser gives identical node id for same object in that position. That's the point.

I use TracePoint to set the source code to SCRIPT_LINES__ before evaluate irb input.

The TracePoint work at here.

    # Evaluate the given +statements+ within the  context of this workspace.
    def evaluate(context, statements, file = __FILE__, line = __LINE__)
      eval(statements, @binding, file, line)
    end

https://github.com/ruby/ruby/blob/v2_6_3/lib/irb/workspace.rb#L83-L86

Hava a fun!

Ruby 2.6 new feature: refine `#to_proc`

Seiei Miyagi — Mon, 04 Mar 2019 12:10:57 +0000

Refinements take place at block passing. [Feature #14223]
https://github.com/ruby/ruby/blob/v2_6_0/NEWS

It's very useful when you want to use the literals as DSL for the block.
Following example refines Integer#to_proc and Array#to_proc to slice the values.

using Module.new {
  refine(Integer) do
    def to_proc
      -> o { o[self] }
    end
  end

  refine(Array) do
    def to_proc
      # Same as -> o { map(&o.method(:[]) }
      # https://dev.to/hanachin/ruby-27-new-feature-method-reference-operator-38l2
      -> o { map(&o.:[]) }
    end
  end
}

p "foo".match(/(a)(b)(c)/)&.then(&1) #=> nil
p "abc".match(/(a)(b)(c)/)&.then(&1) #=> "a"
p "abc".match(/(a)(b)(c)/)&.then(&[1]) #=> ["a"]
p "abc".match(/(a)(b)(c)/)&.then(&[1,2,3]) #=> ["a","b","c"]

How to minimize RSpec `describe`/`context` nesting

Seiei Miyagi — Fri, 18 Jan 2019 04:32:59 +0000

Deeply nested specs

Did you ever write the deeply nested code in RSpec?
I wrote a lot honestly.

In the application code, I avoid to write the deeply nested code. It's hard to read and hard to change, because of bumpy indentation.
When my collegue do code review, they pointing out the deeply nested code.
But in the RSpec, sometime (always) I wrote the deeply nested code and that passed the code review.

For example, like below:

RSpec.describe "Screencast player", type: :system do
  context "When user logged in" do
    let(:user) { create(:user) }

    before do
      login_as(user)
    end

    context "When user register the credit card" do
      let(:card) { create(:card) }

      before do
        user.register_credit_card(card)
      end

      context "When there are screencast" do
        before do
          create(:screencast)
        end

        it "can play the screencast"
      end

      context "When theare not any screencast" do
        it "shows the message, 'no such screencast'"
      end
    end

    context "When user does not register the credit card" do
      it "can not play the screencast"
    end
  end

  context "When user is not logged in" do
    it "can not play the screencast"
  end
end

Why it happened?

RSpec is awesome, it can be nest describe/context forever if you want.
Anything that can go wrong will go wrong. ¹
By the way I have the acceptance test written in Gherkin, how it would go?
It's never nested because it doesn't have the syntax for nesting.
https://docs.cucumber.io/gherkin/reference/

How to fix it?

May the Gherkin be with you.

If you writing the specs like Gherkin, the specs behaves like Gherkin.
It never and ever nested, yay!

How to do it?

I use the above example to explain how to do it.

First move arranging preconditions into the shared_context.

RSpec.describe "Screencast player", type: :system do
  shared_context "When user logged in" do
    let(:user) { create(:user) }

    before do
      login_as(user)
    end
  end

  shared_context "When user register the credit card" do
    let(:card) { create(:card) }

    before do
      user.register_credit_card(card)
    end
  end

  shared_context "When there are screencast" do
    before do
      create(:screencast)
    end
  end
end

Then combine them

RSpec.describe "Screencast player", type: :system do
  shared_context "When user logged in" do
    let(:user) { create(:user) }

    before do
      login_as(user)
    end
  end

  shared_context "When user register the credit card" do
    let(:card) { create(:card) }

    before do
      user.register_credit_card(card)
    end
  end

  shared_context "When there are screencast" do
    before do
      create(:screencast)
    end
  end

  describe "user play the screencast" do
    include_context "When user logged in"
    include_context "When user register the credit card"
    include_context "When there are screencast"

    it "can play the screencast"
  end

  describe "user knows there are no screencast yet" do
    include_context "When user logged in"
    include_context "When user register the credit card"

    it "shows the message, 'no such screencast'"
  end

  describe "user can not play the screencast before register the credit card" do
    include_context "When user logged in"

    it "can not play the screencast"
  end

  describe "user can not play the screencast before logged in" do
    it "can not play the screencast"
  end
end

That's it!

Conclusion

Thank shared_context for fixing my deeply nested specs.

And Gherkin is awesome <3

https://en.wikipedia.org/wiki/Murphy%27s_law ↩

Reverted Ruby 2.7 new feature: Method reference operator

Seiei Miyagi — Sat, 05 Jan 2019 23:08:26 +0000

2019/11/12 reverted

👋

https://github.com/ruby/ruby/commit/fb6a489af2765a3b56e301adf0019af6bbad6156
https://bugs.ruby-lang.org/issues/16275

Method reference operator

New operator .: was added.
https://bugs.ruby-lang.org/issues/12125
https://github.com/ruby/ruby/commit/67c574736912003c377218153f9d3b9c0c96a17b

It converts the method to Method object like method method.

42.:to_s
# => #<Method: Integer#to_s>

What is `method` method?

It converts the method to Method object.
https://docs.ruby-lang.org/en/trunk/Object.html#method-i-method

42.method(:to_s)
# => #<Method: Integer#to_s>

What is `Method` object?

Method object is a pair of receiver and the method, it's callable like a Proc.
https://docs.ruby-lang.org/en/trunk/Method.html

meth = 42.method(:to_s)
# => #<Method: Integer#to_s>
meth.receiver
# => 42
meth.name
# => :to_s
meth.call
# => "42"
meth.call(16)
# => "2a"

What is the differrence between Method reference operator `.:` and `method` method?

If method method is overwritten, .: still work.

class Object
  def method(*); end
end

42.method(:to_s)
# => nil
42.:to_s
# => #<Method: Integer#to_s>

Even if method method is refined, .: still work.

using Module.new {
  refine(Object) do
    def method(*); end
  end
}

42.method(:to_s)
# => nil
42.:to_s
# => #<Method: Integer#to_s>

Is it possible to convert refined method to `Method`?

using Module.new {
  refine(Object) do
    def foo(*); end
  end
}

42.:foo
# undefined method `foo' for class `Integer' (NameError)

How to convert the unary method to `Method`?

Add the suffix @ like method method argument.

42.method(:-@).call
# => -42
42.:-@.call
# => -42

Is it useful?

YES! It is useful for the API which takes the block, like methods in Enumerable.

[1,2,3].map { |n| 2 * n }
# => [2, 4, 6]
[1,2,3].map(&2.:*)
# => [2, 4, 6]


["NG"].any? { |word| "COPYING".include?(word) }
# => true
["NG"].any?(&"COPYING".:include?)
# => true

require "prime"

(1..10).select { |n| Prime.prime?(n) }
# => [2, 3, 5, 7]
(1..10).select(&Prime.:prime?)
# => [2, 3, 5, 7]

Conclusion

You can use new syntax Method reference operator .: now <3

$ rbenv install 2.7.0-dev
$ rbenv global 2.7.0-dev
$ ruby -e 'self.:puts.("Enjoy!")'
Enjoy!

Use Kotlin's / groovy's `it` in Ruby

Seiei Miyagi — Wed, 18 Jul 2018 04:27:40 +0000

I made a gem "thats_it", with this gem, you can use it method to get a single parameter of the block.

require "thats_it"

p [1, 2, 3].map { it * 2 }
# [2, 4, 6]

https://github.com/hanachin/thats_it/

How it works?

Basic idea is rewrites the block's iseq before call it.

# rewrites this block ↓
[1, 2, 3].map { it * 2 }

#          to this ↓
[1, 2, 3].map {|it| it * 2 }

I wrote a implementation details in Japanese.
https://qiita.com/hanachin_/items/8df68325142d46a7fb0b

If you interested, you can read through Google translate.
https://translate.google.com/translate?hl=ja&sl=ja&tl=en&u=https%3A%2F%2Fqiita.com%2Fhanachin_%2Fitems%2F8df68325142d46a7fb0b

How to define the method for the DSL configuration file

Seiei Miyagi — Sun, 31 Dec 2017 04:53:01 +0000

You can define the method for the DSL configuration file¹ by Refinements.

For example, the hi method in a following code can use only in this Rakefile, it shouldn't affect any code outside of the Rakefile.

# Rakefile
main = self

using Module.new {
  refine(main.singleton_class) do
    def hi
      puts :hi
    end
  end
}

desc 'hi'
task :hi do
  hi
end

% rake hi
hi

Common mistake 1

The following code defines the method at top level.

# Rakefile
def hi
  puts :hi
end

desc 'hi'
task :hi do
  hi
end

Common mistake 2

The following code defines the method at top level.

# Rakefile
desc 'hi'
task :hi do
  def hi
    puts :hi
  end

  hi
end

Common mistake 3

The following code defines the method at top level.


# Rakefile
m = Module.new do
  def hi
    puts :hi
  end
end

desc 'hi'
task :hi do
  include m
  hi
end

Why should we avoid to define the method at top level?

It possibly breaks other libraries code.

For example:

# duck.rb
class Duck < Struct.new(:name)
  def sound
    puts 'quack'
  end
end

# Rakefile
require_relative 'duck.rb'

def puts(*)
  print 'Hi! '
  super
end

desc 'hi'
task :hi do
  duck = Duck.new('Donald')
  puts duck.name
  duck.sound
end

$ rake hi
Hi! Donald
Hi! quack

The benefit of the Refinements

The ruby's Refinements are lexical in scope².
Thus the top level method that defined by the Refinements couldn't breaks other libraries code, It's totally fine!

# Rakefile
require_relative 'duck.rb'

main = self

using Module.new {
  refine(main.singleton_class) do
    def puts(*)
      print 'Hi! '
      super
    end
  end
}

desc 'hi'
task :hi do
  duck = Duck.new('Donald')
  puts duck.name
  duck.sound
end

$ rake hi
Hi! Donald
quack

Other approach

Wrap the method and DSLs within a module.

# Rakefile
require_relative 'duck.rb'

Module.new {
  def puts(*)
    print 'Hi!, '
    super
  end
  extend(self)

  extend Rake::DSL

  desc 'hi'
  task :hi do
    duck = Duck.new('Donald')
    puts duck.name
    duck.sound
  end
}

$ rake hi
Hi!, Donald
quack

e.g. Rakefile, config/routes.rb, unicorn.rb, etc... ↩
https://docs.ruby-lang.org/en/trunk/syntax/refinements_rdoc.html#label-Scope ↩

DEV Community: Seiei Miyagi

Apply Reference table to the Rails STI type/Polymorphic type/enum/inclusion validated columns

Sample repository

How to do

Conclusion

Quine Snake Battle

How to play

CircleCI Workflows to rerun flaky RSpec examples

Sample project

Conclusion

How to define almost global variable and almost top level method in Rails

Optimize boot time of ruby CLI tools

Using RubyVM::AbstractSyntaxTree.of in pry

How can I use RubyVM::AbstractSyntaxTree.of in irb?

But how does it work?

Ruby 2.6 new feature: refine `#to_proc`

How to minimize RSpec `describe`/`context` nesting

Deeply nested specs

Why it happened?

How to fix it?

How to do it?

Conclusion

Reverted Ruby 2.7 new feature: Method reference operator

2019/11/12 reverted

Method reference operator

What is method method?

What is Method object?

What is the differrence between Method reference operator .: and method method?

Is it possible to convert refined method to Method?

How to convert the unary method to Method?

Is it useful?

Conclusion

Use Kotlin's / groovy's `it` in Ruby

How it works?

How to define the method for the DSL configuration file

Common mistake 1

Common mistake 2

Common mistake 3

Why should we avoid to define the method at top level?

The benefit of the Refinements

Other approach

What is `method` method?

What is `Method` object?

What is the differrence between Method reference operator `.:` and `method` method?

Is it possible to convert refined method to `Method`?

How to convert the unary method to `Method`?