Add rule discouraging instance_variable_get and instance_variable_set

README.adoc

@@ -5790,6 +5790,39 @@ class Person
 end
 ----
 
+=== Avoid Dynamic Instance Variable Access [[no-dynamic-instance-variable-access]]
+
+Avoid `instance_variable_get` and `instance_variable_set`.
+These methods bypass encapsulation and couple callers to internal implementation details.
+Prefer defining explicit accessor methods instead.
+Framework or library code that needs to work generically with arbitrary objects may be a justified exception.
+
+[source,ruby]
+----
+# bad
+class Person
+  def initialize(name)
+    @name = name
+  end
+end
+
+person = Person.new('Alice')
+person.instance_variable_get(:@name) # => 'Alice'
+person.instance_variable_set(:@name, 'Bob')
+
+# good
+class Person
+  attr_reader :name
+
+  def initialize(name)
+    @name = name
+  end
+end
+
+person = Person.new('Alice')
+person.name # => 'Alice'
+----
+
 === No Monkey Patching [[no-monkey-patching]]
 
 Do not mess around in core classes when writing libraries (do not monkey-patch them).