[RAILS] Do not return when memoizing in Ruby

The bottom line is that you shouldn't make an early return when memoizing in Ruby (probably not just in Ruby).

• NG

def user
  @user ||= begin
    user = User.find_or_initialize_by(id: 1)
    return user if user.persisted? #Do not return while defining instance variables
    
    user.save
    user
  end
end

• OK

def user
  @user ||= begin
    user = User.find_or_initialize_by(id: 1)
    if user.persisted?
      user
    else
      user.save
      user
    end
  end
end

#Or

def user
  @user ||= begin
    user = User.find_or_initialize_by(id: 1)
    user.save if user.new_record?
    user
  end
end

When using memoization in Ruby (Rails), I think that you may write as follows.

def user
  @user ||= User.first
end

If there are multiple lines, enclose them in begin ~ ʻend`.

def user
  @user ||= begin
    user = user.find_or_initialize_by(id: 1)
    if user.persisted?
      user
    else
      user.save
      user
    end
  end
end

Let's use early return, which is a common refactoring technique.

def user
  @user ||= begin
    user = User.find_or_initialize_by(id: 1)
    return user if user.persisted?
      
    user.save
    user
  end
end

At first glance, it looks good, but when I run this method in the rails console, it looks like this:

[1] pry(main)> def user
[1] pry(main)*   @user ||= begin
[1] pry(main)*     user = User.find_or_initialize_by(id: 1)
[1] pry(main)*     return user if user.persisted?
[1] pry(main)*
[1] pry(main)*     user.save
[1] pry(main)*     user
[1] pry(main)*   end
[1] pry(main)* end
=> :user

[2] pry(main)> user
  User Load (3.4ms)  SELECT `users`.* FROM `users` WHERE `users`.`id` = 1 LIMIT 1
=> #<User:0x00007ff0b4d2e338
 id: 1,
 created_at: Tue, 09 Jun 2020 15:04:04 JST +09:00,
 updated_at: Tue, 09 Jun 2020 15:04:04 JST +09:00>
[3] pry(main)> user
  User Load (1.8ms)  SELECT `users`.* FROM `users` WHERE `users`.`id` = 1 LIMIT 1
=> #<User:0x00007ff0ad554740
 id: 1,
 created_at: Tue, 09 Jun 2020 15:04:04 JST +09:00,
 updated_at: Tue, 09 Jun 2020 15:04:04 JST +09:00>

No memoization is done and a query is issued every time. If you check the reference again,

Ruby 2.7.0 Reference Manual https://docs.ruby-lang.org/ja/latest/doc/spec=2fcontrol.html#return return Ends the method execution with the value of the expression as the return value.

Because it says, the ʻuser method ends at the stage of return, and the instance variable of @ user remains nil`, so the process is executed every time. It's natural when you think about it, but be careful because you may get addicted to writing that you often use early returns in your habit.