def_method_missing

gistfile1.rb

class Foo
  # regexp matchers yield the MatchData to the block, so you can modify the method
  # body based on the regexp
  def_method_missing /bar/ do |match|
    -> { match.pre_match }
  end

  # without a regexp matcher, the name of the method is passed to the block, allowing
  # you to decide whether or not to implement the method
  def_method_missing do |name|
    -> { name } if name.length == 4
    -> { "bang!" } if name[-1] == '!'
  end
end

foo = Foo.new

# regexp-based method_missing
foo.respond_to?(:bazbar)      # => true
foo.bazbar                    # => "baz"
foo.methods.include? /bazbaz/ # => true

# arbitrary Ruby method_missing
foo.respond_to?(:wat)       # => false
foo.respond_to?(:what)      # => true
foo.what                    # => :what
foo.methods.include?(:what) # => true

foo.bang  # => :bang # matches four-character method name
foo.bang! # => "bang!" # matches last-character bang
foo.wat!  # => :wat! # matches four-character method name first