Block,Interator............................

# 
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mystring="aaa"
puts mystring.empty?
class P
def a
yield(ok.empty?)
end
end
class PP
def myclass_b
P.a {|arg|; puts arg}
end
end

class A
def mycool
  yield
end
def mycool_yield
  A.mycool{puts "OK"}
end
  
end

 The "yield" method is just like the "invoke".  But it could do a more little job......