Code points to binaries in Elixir

A code point is a numerical representation of a character in the Unicode Standard. Elixir uses UTF-8 to encode strings and binaries.

For example, code point for letter ę equals to 281:

iex(1)> ?ę

Here is how UTF-8 encoding serializes numbers on multiple bytes:

Length First byte Following bytes
Single byte 0XXXXXXX N/A
Two bytes 110XXXXX 10XXXXXX
Three bytes 1110XXXX 10XXXXXX
Four bytes 11110XXX 10XXXXXX

Our 281 code point requires 2 bytes for representation in UTF-8 encoding (a single UTF-8 byte can encode numbers from 0 to 127 only).

If we convert 281 straight to a binary, we will receive 100011001. Placing this sequence of 1/0 on placeholders for two-bytes length from the table above gives the following bytes: 11000100 11011001. In the base-10 system, they are represented as 196 and 153 which are our binaries:

iex(2)> "ę" <> <<0>>
<<196, 153, 0>>
iex(3)> "foo" <> <<0>>
<<102, 111, 111, 0>>

Concatenating a string with with the null byte <<0>> returns its inner binary representation.