irb(main):001:0> class A
irb(main):002:1> def a
irb(main):003:2> p 'hello world'
irb(main):004:2> end
irb(main):005:1> end
=> nil
irb(main):006:0>
irb(main):007:0* a = A.new
=> #<A:0x0000001fbee140>
irb(main):008:0> a.instance_eval do
irb(main):009:1* alias :b :a
irb(main):010:1> def a
irb(main):011:2> p 'you should not use this method'
irb(main):012:2> end
irb(main):013:1> end
=> nil
irb(main):014:0> a.a
"you should not use this method"
=> "you should not use this method"
irb(main):015:0> a.b
"hello world"
=> "hello world"