Hi Friedger, what about converting a double to string than appending the double to a blank string? Any better way for that too?

Oops! Thanks Friedger

To convert a String (or, more generally, a StringInterface) to a ByteVec (aka {FastArray-of byte}) or ByteArray (aka {Array-of byte}) you will probably want to specify the character encoding you want to use. You can then use a TranscodingTextOutputStream to encode the characters and write them into a ByteArray through a ByteArrayOutputStream:

{define-proc {string-to-bytes string:StringInterface}:ByteArray
  def bytes = {ByteArray}
  {with-open-streams
     out = {TranscodingTextOutputStream
                 {ByteArrayOutputStream bytes},
                 CharEncoding.utf8
           }
  do
     {out.write-one-string string}
  }
  {return bytes}
}

If you know the size of the byte vec you need you can just use the built-in 'encode-characters' function to do this. If you don't mind the vector having wasted space in it you can write:

def bytes = {ByteVec max-size = string.size * char-encoding.transcoding-max-expansion-factor}
{encode-characters string, bytes, char-encoding}

Friedger's trick will work but is a little slow and does not specify the character encoding -- I think it will use UTF8, but I am not sure.

(I haven't tested any of this code, but I think it is correct.)