Add `Kernel#yield_self`; CRuby2.5
ADD
mrbgems/mruby-kernel-ext/mrblib/kernel.rb
+module Kernel
+ # call-seq:
+ # obj.yield_self {|_obj|...} -> an_object
+ #
+ # Yields <i>obj</i> and returns the result.
+ #
+ # 'my string'.yield_self {|s|s.upcase} #=> "MY STRING"
+ #
+ def yield_self(&block)
+ return to_enum :yield_self unless block
+ block.call(self)
+ end
+end

Add `Kernel#yield_self`; CRuby2.5