Add Define A Method On A Struct as a Ruby til

ruby/define-a-method-on-a-struct.md

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+# Define A Method On A Struct
+
+When defining a Ruby `Struct`, you can optionally pass it a block that defines
+any number of methods as instance methods on that `Struct`. They can reference
+the attributes of the `Struct`.
+
+Here is an example of a person `Struct` with a `full_name` method that uses the
+`first_name` and `last_name` attributes.
+
+```ruby
+Person = Struct.new(:first_name, :last_name, :age) do
+  def full_name
+    "#{first_name} #{last_name}"
+  end
+end
+```
+
+This `Struct` can be used like so:
+
+```ruby
+> liz = Person.new("Liz", "Lemon", 39)
+=> #<struct Person first_name="Liz", last_name="Lemon", age=39>
+> liz.full_name
+=> "Liz Lemon"
+```
+
+This is a great way to make a `Struct` just a bit more powerful without having
+to convert it into a full-blown PORO (plain old Ruby object).