Ruby Pattern Matching Shenanigans

pm.rb

def example(label)
  puts "## #{label}"
  yield
  puts
  puts
end

example("Foo.===(v)") do
  class Foo
    def self.===(v)
      puts "Foo.==="
      v == "hello"
    end
  end

  case "hello"
  in Foo
    puts "Foo"
  else
    puts "Not Foo"
  end
end

example("Foo#===(v)") do
  class Foo
    def ===(v)
      puts "Foo#==="
      v == "hello"
    end
  end

  case "hello"
  when Foo.new
    puts "Foo"
  else
    puts "Not Foo"
  end
end

example("Proc-based") do
  case "hello"
  in ->(x) {
    puts "Proc"
    true
  }
    puts "Foo"
  else
    puts "Not Foo"
  end
end

example("Override Object and match per pattern") do
  class Object
    def in(pattern)
      puts "in"
      pattern === self
    end
  end

  if "hello".in(Foo.new)
    puts "Foo"
  elsif "hello".in(Foo)
    puts "Foo"
  else
    puts "Not Foo"
  end
end