Add Define A Set Of Class Methods as a Ruby TIL

ruby/define-a-set-of-class-methods.md

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+# Define A Set Of Class Methods
+
+The most common way to define class methods is by defining them directly with
+`self` (the class in the current context) on a method by method basis:
+
+```ruby
+class User
+  def self.find_by(attrs)
+    # lookup logic ...
+  end
+end
+```
+
+If you have a group of class methods you want to define, you can stick them all
+within a `class << self` block which does similarly defines each of them as
+singleton methods of that class (`User` in this case):
+
+```ruby
+class User
+  class << self
+    def find_by_email(email)
+      # lookup logic ...
+    end
+
+    def find_by_last_name(last_name)
+      # lookup logic ...
+    end
+  end
+end
+```
+
+This opens the singleton class of `User` for modification, adding these two new
+methods.
+
+We can see those defined alongside all other direct and inherited class methods:
+
+```ruby
+> User.methods
+=>
+[:find_by_email,
+ :find_by_last_name,
+ :yaml_tag,
+ :allocate,
+ ...
+]
+```