Illustration of Rubinius Encoding Issues with String Interpolation

test.rb

str = "a utf-8 string (\u20AC) with utf-8 chars".force_encoding("utf-8")
str2 = "This string is #{str} but looks like ascii-only"
puts "str: #{str}"
puts "str.ascii_only?: #{str.ascii_only?}" # => false
puts "str2: #{str2}"
puts "str2 encoding: #{str2.encoding}" # => UTF-8
puts "str2.ascii_only?: #{str2.ascii_only?}" # => true
puts "str2.dup.ascii_only?: #{str2.dup.ascii_only?}"
puts "<< broken encoding:"
str3 = "an ascii string with "
puts "str3: #{str3}"
puts "str3 encoding: #{str3.encoding}"
puts "str3 << str2"
str3 << str2
puts "str3: #{str3}"
puts "str3 encoding: #{str3.encoding}"