I have the following file:
# encoding: UTF-8
a = 1 << 7
puts a.chr.encoding
ASCII-8BIT
UTF-8
chr
has a encoding parameter, defaulting to ASCII, when char is < 0xff
(there UTF is identical to ASCII):
128.chr.encoding # => #<Encoding:ASCII-8BIT>
255.chr.encoding # => #<Encoding:ASCII-8BIT>
256.chr.encoding # => RangeError: 256 out of char range
Encoding.default_internal = Encoding::UTF_8
255.chr.encoding # => #<Encoding:ASCII-8BIT>
256.chr.encoding # => #<Encoding:UTF-8>
128.chr(Encoding::UTF_8).encoding # => #<Encoding:UTF-8>
500.chr(Encoding::UTF_8).encoding # => #<Encoding:UTF-8>