Ruby 2.7の新機能メソッド参照演算子 ref: https://qiita.com/hanachin_/items/1aa1ba38a87dee91aed6

file0.txt

123.method(:to_s)
# => #<Method: Integer#to_s>

file1.txt

meth = 123.method(:to_s)
# => #<Method: Integer#to_s>
meth.call
# => "123"
meth.call(16)
# => "7b"

file2.txt

123.:to_s
# => #<Method: Integer#to_s>

file3.txt

class Object
  def method(*)
    nil
  end
end

123.method(:to_s)
# => nil

123.:to_s.call
# => "123"

file4.txt

using Module.new {
  refine(Object) do
    def method(*); end
  end
}
method(:puts)
# => nil
self.:puts
# => #<Method: main.puts>

file5.txt

using Module.new {
  refine(Object) do
    def method(*); end
  end
}
self.:method.call(:puts).call(1)
# 1

file6.txt

1.method(:-@).call
# => -1
1.:[email protected]
# => -1

file7.txt

[1,2,3].map(&2.:*)
# => [2, 4, 6]

["エロ"].any?(&"イエロー".:include?)
# => true

require "prime"
(1..10).select(&Prime.:prime?)
# => [2, 3, 5, 7]