Fixed order of method in line 12 & remove comments

app/models/user.rb

 class User < ApplicationRecord
-  def User.digest(string)
-    cost = ActiveModel::SecurePassword.min_cost ? BCrypt::Engine::MIN_COST :
-    BCrypt::Engine.cost
-    BCrypt::Password.create(string, cost: cost)
-  end
-
-# Constant
   VALID_EMAIL_REGEX = /\A[\w+\-.]+@[a-z\d\-.]+\.[a-z]+\z/i
 
-# Validation macros
   validates :email, presence: true, length: { maximum: 255 }, format: { with: VALID_EMAIL_REGEX }
   validates :name, presence: true, length: { maximum: 50 }, uniqueness: { case_sensitive: false }
   validates :password, presence: true, length: { minimum: 6 }
@@ -16,4 +8,9 @@ class User < ApplicationRecord
   before_save { email.downcase! } #Call Backs
   
   has_secure_password
+
+  def User.digest(string)
+    cost = ActiveModel::SecurePassword.min_cost ? BCrypt::Engine::MIN_COST : BCrypt::Engine.cost
+    BCrypt::Password.create(string, cost: cost)
+  end
 end