[ruby-core:55986] Re: [ruby-trunk - Bug #8630][Open] Transcoding high-bit bytes from ASCII-8BIT to a text encoding should be :invalid, not :undef

2013/7/13 headius (Charles Nutter) <[e-mail]>:
> Bug #8630: Transcoding high-bit bytes from ASCII-8BIT to a text encoding should be :invalid, not :undef
> https://bugs.ruby-lang.org/issues/8630

> When transcoding from ASCII-8BIT (BINARY) to a text encoding (e.g. UTF-8), MRI will raise an error for high-bit bytes:
>
> "\xC3".encode("utf-8", "binary") # => Encoding::UndefinedConversionError
>
> This can be disabled by passing :undef => :replace as an option to the encode call.
>
> I believe that "undef" is the wrong treatment for this error. Undef means that the input character has no representation in the target encoding. In this case, the error is raised because only US-ASCII range of bytes are *valid* for transcoding, so the transcoding of high-bit bytes is by definition *invalid*, not undefined. In other words, high-bit bytes in ASCII-8BIT/BINARY are *invalid* as characters.

No.

ASCII-8BIT consists 128 ASCII characters and 128 special characters to
represent 0x80 to 0xff binary bytes.
The special characters are not representable in UTF-8.
So UndefinedConversionError is raised.

The validity of a characetr is defined by encoding, not transcoding.
-- 
Tanaka Akira