Add Check If An Object Includes A Module as a Ruby til

ruby/check-if-an-object-includes-a-module.md

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+# Check If An Object Includes A Module
+
+You may want to know if an object's class includes a module because that will
+tell you something about the object's behavior. It is another way of asking if
+an object responds to a method or set of methods, assuming you know what
+methods the module provides.
+
+This can be done with the [`Module#include?`
+method](https://ruby-doc.org/core-3.0.0/Module.html#method-i-include-3F).
+
+```ruby
+# assuming some object book of type Book that includes Rateable
+> book.class
+=> Book
+> book.class.include?(Rateable)
+=> true
+
+# assuming some object author of type Author that doesn't include Rateable
+> author.class
+=> Author
+> author.class.include?(Rateable)
+=> false
+```
+
+[source](https://stackoverflow.com/a/28667632/535590)